Metalorganic chemical vapor deposition of HgCdTe p/n junctions using arsenic and iodine doping

We report new results on metalorganic chemical vapor deposition (MOCVD)in situ growth of long wavelength infrared (LWIR) P-on-n and medium wavelength infrared (MWIR) n-on-P HgCdTe heterojunction photodiodes using the interdiffused multilayer process (IMP). The n-type regions are doped with iodine using the precursor ethyl iodide (El). I-doped HgCdTe using El has mobilities higher than that obtained on undoped background annealed films and are comparable to LPE grown In-doped HgCdTe. The p-type layers are doped with arsenic from either tertiarybutylarsine (TBAs) or a new precursor,tris-dimethylaminoarsenic (DMAAs). The substrates used in this work are lattice matched CdZnTe oriented (211)B or (100)4°→«110». Junction quality was assessed by fabricating and characterizing backside-illuminated arrays of variable-area circular mesa photodiodes. This paper presents four new results. First, carrier lifetimes measured at 80K on arsenic doped single HgCdTe layers are generally longer for films doped from the new precursor DMAAs than from TBAs. Second, we present data on the first P-on-n HgCdTe photodiodes grownin situ with DMAAs which have R₀A products limited by g-r current at 80K for λ_co = 7–12 μm, comparable to the best R₀A products we have achieved with TBAs. Third, we report the first experimental data on a new HgCdTe device architecture, the n-on-P heterojunction, with a wide gap p-type layer which allows radiation incident through the substrate to be absorbed in a narrower gap n-type layer, thereby eliminating interface recombination effects. With the n-on-P architecture, MWIR photodiodes were obtained reproducibly with classical spectral response shapes, high quantum efficiencies (70-75%) and R₀A products above 2 x 10⁵ ohm-cm² for λ_co = 5.0 μm at 80K. Fourth, we report 40K data for LWIR P-on-n HgCdTe heterojunction photodiodes (using TBAs), with R₀A values of 2 x 10⁴ ohm-cm² for λ_co = 11.7 μm and 5 x 10⁵ ohm-cm² for λ_co - 9.4 μm. These are the highest R₀A values reported to date for LWIR P-on-n heterojunctions grownin situ by MOCVD.     

Status of the MBE technology at leti LIR for the manufacturing of HgCdTe focal plane arrays

This paper presents recent developments that have been made in Leti Infrared Laboratory in the field of molecular beam epitaxy (MBE) growth and fabrication of medium wavelength and long wavelength infrared (MWIR and LWIR) HgCdTe devices. The techniques that lead to growth temperature and flux control are presented. Run to run composition reproducibility is investigated on runs of more than 15 consecutively grown layers. Etch pit density in the low 10⁵ cm⁻² and void density lower than 10³ cm⁻² are obtained routinely on CdZnTe substrates. The samples exhibit low n-type carrier concentration in the 10¹⁴ to 10¹⁵ cm⁻³ range and mobility in excess of 10⁵ cm²/Vs at 77 K for epilayers with 9.5 μm cut-off wavelength. LWIR diodes, fabricated with an-on-p homojunction process present dynamic resistance area products which reach values of 8 10³ Ωcm² for a biased voltage of −50 mV and a cutoff wavelength of 9.5 μm at 77 K. A 320 × 240 plane array with a 30 μm pitch operating at 77 K in the MWIR range has been developed using HgCdTe and CdTe layers MBE grown on a Germanium substrate. Mean NEDT value of 8.8 mK together with an operability of 99.94% is obtained. We fabricated MWIR two-color detectors by the superposition of layers of HgCdTe with different compositions and a mixed MESA and planar technology. These detectors are spatially coherent and can be independently addressed. Current voltage curves of 60 × 60 μm² photodiodes have breakdown voltage exceeding 800 mV for each diode. The cutoff wavelength at 77 K is 3.1 μm for the MWIR-1 and 5 μm for the MWIR-2.     

A 5 mm×5 mm mid-wavelength infrared HgCdTe photodiode array with negative luminescence efficiency ∼95%

The negative luminescence (NL) efficiency of a 5 mm×5 mm array (100% effective fill factor) of HgCdTe photodiodes (λ_co=4.8 μm at 295 K) has been measured as a function of temperature. The internal NL efficiency of ≈95% at λ=4 μm is nearly independent of temperature in the 240–300 K range and, at 300 K, corresponds to an apparent temperature reduction of 60 K. This performance is obtained at a reverse-bias saturation-current density of only 0.11 A/cm² at 296 K. With large area, high efficiency, and low saturation-current density, our results demonstrate a level of NL device performance at which such applications as cold shields for large-format focal plane arrays (FPAs) and multipoint nonuniformity correctors appear practical.     

Advances in large-area Hg1−xCdxTe photovoltaic detectors for remote-sensing applications

State-of-the-art large-area photovoltaic (PV) detectors fabricated in HgCdTe grown by molecular beam epitaxy (MBE) have been demonstrated for the Crosstrack Infrared Sounder (CrIS) instrument. Large-area devices (1 mm in diameter) yielded excellent electrical and optical performance operating at 81 K for λ_c ∼ 15 μm, at 98 K for λ_c ∼ 9 μm, and λ_c ∼ 5-μm spectral cutoffs. Fabricated detectors have near-theoretical electrical performance, and Anti Reflection coated quantum efficiency (QE) is greater than 0.70. Measured average R₀A at 98 K is 2.0E7 Ωcm², and near-theoretical QEs greater than 0.90 were obtained on detectors with λ_c ∼ 5-μm spectral cutoffs. These state-of-the-art large-area PV detector results reflect high-quality HgCdTe grown by MBE on CdZnTe substrates in all three spectral bands of interest.     

MBE P-on-n Hg1−xCdxTe heterostructure detectors on silicon substrates

The capability of growing state-of-the-art middle wavelength infrared (MWIR)-HgCdTe layers by molecular beam epitaxy (MBE) on large area silicon substrates has been demonstrated. We have obtained excellent compositional uniformity with standard deviation of 0.001 with mean composition of 0.321 across 1.5″ radii. R₀A as high as 5 × 10⁷ ω-cm² with a mean value of 7 × 10⁶ Θ-cm² was measured for cut-off wavelength of 4.8 μm at 77K. Devices exhibit diffusion limited performance for temperatures above 95K. Quantum efficiencies up to 63% were observed (with no anti-reflection coating) for cut-off wavelength (4.8–5.4) μm @ 77K. Excellent performance of the fabricated photodiodes on MBE HgCdTe/CdTe/Si reflects on the overall quality of the grown material in the MWIR region.     

Uniform low defect density molecular beam epitaxial HgCdTe

This paper describes recent advances in MBE HgCdTe technology. A new 3 inch production molecular beam epitaxy (MBE) system, Riber Model 32P, was installed at Rockwell in 1994. The growth technology developed over the years at Rockwell using the Riber 2300 R&D system was transferred to the 32P system in less than six months. This short period of technology transfer attests to our understanding of the MBE HgCdTe growth dynamics and the key growth parameters. Device quality material is being grown routinely in this new system. Further advances have been made to achieve better growth control. One of the biggest challenges in the growth of MBE HgCdTe is the day-to-day control of the substrate surface temperature at nucleation and during growth. This paper describes techniques that have led to growth temperature reproducibility within + - 1°C, and a variation in temperature during substrate rotation within 0.5°C. The rotation of the substrate during growth has improved the uniformity of the grown layers. The measured uniformity data on composition for a typical 3 cm × 3 cm MBE HgCdTe/CdZnTe shows the average and standard deviation values of 0.229 and 0.0006, respectively. Similarly, the average and standard deviation for the layer thickness are 7.5 and 0.06 μm, respectively. P-on-n LWIR test structure photodiodes fabricated using material grown by the new system and using rotation during growth have resulted in high-performance (R₀)A, quantum efficiency) devices at 77 and 40K. In addition, 128 × 28 focal plane arrays with excellent performance and operability have been demonstrated.     

Development of Molecular Beam Epitaxially Grown Hg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te for High-Density Vertically-Integrated Photodiode-Based Focal Plane Arrays

Hg_1−x Cd _x Te samples of x ~ 0.3 (in the midwave infrared, or MWIR, spectral band) were prepared by molecular beam epitaxy (MBE) for fabrication into 30-μm-pitch, 256 × 256, front-side-illuminated, high-density vertically-integrated photodiode (HDVIP) focal plane arrays (FPAs). These MBE Hg_1−x Cd _x Te samples were grown on CdZnTe(211) substrates prepared in this laboratory; they were ~10-μm thick and were doped with indium to ~5 × 10¹⁴ cm⁻³. Standard HDVIP process flow was employed for array fabrication. Excellent array performance data were obtained from these MWIR arrays with MBE HgCdTe material. The noise-equivalent differential flux (NEΔΦ) operability of the best array is 99.76%, comparable to the best array obtained from liquid-phase epitaxy (LPE) material prepared in this laboratory.     

Metalorganic chemical vapor deposition of HgCdTe for photodiode applications

Metalorganic chemical vapor depositon (MOCVD) in situ growth of p-on-n junctions for long wavelength infrared (LWIR) and medium wavelength infrared (MWIR) photodiodes is reported. The interdiffused multilayer process was used for the growth of the HgCdTe junctions on CdTe and CdZnTe substrates. The n-type region was grown undoped while the p-type layer was arsenic doped using tertiarybutylarsine. Following a low temperature anneal in Hg vapor, carrier densities of (0.2-2) x 10¹⁵ cm³ and mobilities of (0.7-1.2) x 10⁵ cm²/V-s were obtained for n-type LWIR (x ~ 0.22) layers at 80K. Carrier lifetimes of these layers at 80 K are ~l-2 μs. For the p-type region arsenic doping was controlled in the range of (1-20) x 10¹⁶ cm^-3. Arsenic doping levels in the junctions were determined by calibrated secondary ion mass spectroscopy depth profile measurements. Composition and doping of the p-on-n heterojunctions could be independently controlled so that the electrical junction could be located deeper than the change in the composition. The graded composition region between the narrow and wide (x = 0.28-0.30) bandgap regions are 1–2 μm depending on the growth temperature. Backside-illuminated variable-area circular mesa photodiode arrays were fabricated on the grown junctions as well as on ion implanted n-on-p MWIR junctions. The spectral responses are classical in shape. Quantum efficiencies at 80K are 42–77% for devices without anti-reflection coating and with cutoff wavelengths of 4.8–11.0 μm. Quantum efficiencies are independent of reverse bias voltage and do not decrease strongly at lower temperatures indicating that valence band barrier effects are not present. 80K R_oA of 15.9 Ω-cm² was obtained for an array with 11.0 μm cutoff. Detailed measurements of the characteristics of the MOCVD in situ grown and implanted photodiodes are reported.     

Latest Developments of HgCdTe e-APDs at CEA LETI-Minatec

In this communication, we report on the electro-optical characterization of planar back-side-illuminated HgCdTe electron initiated avalanche photodiode (e-APD) test arrays with cut-off wavelengths λ _c = 2.4 μm, λ _c = 4.8 μm, and λ _c = 9.2 μm. The e-APDs were manufactured at LETI using absorption layers grown by molecular beam epitaxy (MBE). We present measurements of the distributions in gain, noise, and equivalent input dark current. The mid-wave (MW) diodes yielded a very low dispersion (2%) and high operability (98%) for gains up to M = 200. The excess noise factor and equivalent input current (I _{eq_in}) operability were slightly lower, due to defects in the depletion region. The lowest measured value of I _{eq_in} = 1 fA corresponds to the lowest level measured so far in HgCdTe e-APDs and opens the way to new applications. The gain in the long-wave (LW) diodes was limited by tunnelling currents to a value of M = 2.4, associated with an average noise factor F = 1.2. A gain of M = 20 at a bias of −22.5 V was demonstrated in the short-wave (SW) e-APDs.     

Independently accessed back-to-back HgCdTe photodiodes: A new dual-band infrared detector

We report the first data for a new two-color HgCdTe infrared detector for use in large dual-band infrared focal plane arrays (IRFPAs). Referred to as the independently accessed back-to-back photodiode structure, this novel dual-band HgCdTe detector provides independent electrical access to each of two spatially collocated back-to-back HgCdTe photodiodes so that true simultaneous and independent detection of medium wavelength (MW, 3–5 μm) and long wavelength (LW, 8–12 μm) infrared radiation can be accomplished. This new dual-band detector is directly compatible with standard backside-illuminated bump-interconnected hybrid HgCdTe IRFPA technology. It is capable of high fill factor, and allows high quantum efficiency and BLIP sensitivity to be realized in both the MW and LW photodiodes. We report data that demonstrate experimentally the key features of this new dual-band detector. These arrays have a unit cell size of 100 x 100 μm², and were fabricated from a four-layer p-n-N-P HgCdTe film grown in situ by metalorganic chemical vapor deposition on a CdZnTe substrate. At 80K, the MW detector cutoff wavelength is 4.5 μm and the LW detector cutoff wavelength is 8.0 μm. Spectral crosstalk is less than 3%. Data confirm that the MW and LW photodiodes are electrically and radiometrically independent.     

LWIR HgCdTe Detectors Grown on Ge Substrates

Long-wavelength infrared (LWIR) HgCdTe p-on-n double-layer heterojunctions (DLHJs) for infrared detector applications have been grown on 100 mm Ge (112) substrates by molecular beam epitaxy (MBE). The objective of this current work was to grow our baseline p-on-n DLHJ detector structure (used earlier on Si substrates) on 100 mm Ge substrates in the 10 μm to 11 μm LWIR spectral region, evaluate the material properties, and obtain some preliminary detector performance data. Material characterization techniques included are X-ray rocking curves, etch pit density (EPD) measurements, compositional uniformity determined from Fourier-transform infrared (FTIR) transmission, and doping concentrations determined from secondary-ion mass spectroscopy (SIMS). Detector properties include resistance-area product (RoA), spectral response, and quantum efficiency. Results of LWIR HgCdTe detectors and test structure arrays (TSA) fabricated on both Ge and silicon (Si) substrates are presented and compared. Material properties demonstrated include X-ray full-width of half-maximum (FWHM) as low as 77 arcsec, typical etch pit densities in mid 10⁶ cm⁻² and wavelength cutoff maximum/minimum variation <2% across the full wafer. Detector characteristics were found to be nearly identical for HgCdTe grown on either Ge or Si substrates.     

MBE HgCdTe on Alternative Substrates for FPA Applications

Results of first-principles calculations and experiments focusing on molecular beam epitaxy (MBE) growth of HgCdTe on the alternative substrates of GaAs and Si are described. The As passivation on (2 × 1) reconstructed (211) Si and its effects on the surface polarity of ZnTe or CdTe were clarified by examining the bonding configurations of As. The quality of HgCdTe grown on Si was confirmed to be similar to that grown on GaAs. Typical surface defects in HgCdTe and CdTe were classified. Good results for uniformities of full width at half maximum (FWHM) values of x-ray rocking curves, surface defects, and x values of Hg_1−x Cd _x Te were obtained by refining the demanding parameters and possible tradeoffs. The sticking coefficient of As₄ for MBE HgCdTe was determined. The effects of Hg-assisted annealing for As activation were investigated experimentally and theoretically by examining the difference of the formation energy of As_Hg and As_Te. Results of focal-plane arrays (FPAs) fabricated with HgCdTe grown on Si and on GaAs are discussed.     

Ten-inch molecular beam epitaxy production system for HgCdTe growth

Growth of Hg_1−xCd_xTe by molecular beam epitaxy (MBE) has been under development since the early 1980s at Rockwell Scientific Company (RSC), formerly the Rockwell Science Center; and we have shown that high-performance and highly reproducible MBE HgCdTe double heterostructure planar p-on-n devices can be produced with high throughput for various single- and multiplecolor infrared applications. In this paper, we present data on Hg_1−xCd_xTe epitaxial layers grown in a ten-inch production MBE system. For growth of HgCdTe, standard effusion cells containing CdTe and Te were used, in addition to a Hg source. The system is equipped with reflection high energy electron diffraction (RHEED) and spectral ellipsometry in addition to other fully automated electrical and optical monitoring systems. The HgCdTe heterostructures grown in our large ten-inch Riber 49 MBE system have outstanding structural characteristics with etch-pit densities (EPDs) in the low 10⁴ cm⁻² range, Hall carrier concentration in low 10¹⁴ cm⁻³, and void density <1000 cm². The epilayers were grown on near lattice-matched (211)B Cd_0.96Zn_0.04Te substrates. High-performance mid wavelength infrared (MWIR) devices were fabricated with R₀A values of 7.2×10⁶ Ω-cm² at 110 K, and the quantum efficiency without an antireflection coating was 71.5% for cutoff wavelength of 5.21 μm at 37 K. For short wavelength infrared (SWIR) devices, an R₀A value of 9.4×10⁵ Ω-cm² at 200 K was obtained and quantum efficiency without an antireflection coating was 64% for cutoff wavelength of 2.61 μm at 37 K. These R₀A values are comparable to our trend line values in this temperature range.     

MWIR DLPH HgCdTe photodiode performance dependence on substrate material

Mid wavelength infrared p-on-n double layer planar heterostructure (DLPH) photodiodes have been fabricated in HgCdTe double layers grown in situ by liquid phase epitaxy (LPE), on CdZnTe and for the first time on CdTe/sapphire (PACE-1). Characterization of these devices shed light on the nature of the material limits on device performance for devices performing near theoretical limits. LPE double layers on CdZnTe and on PACE-1 substrates were grown in a horizontal slider furnace. All the photodiodes are p-on-n heterostructures with indium as the n-type dopant and arsenic the p-type dopant. Incorporation of arsenic is via implantation followed by an annealing step that was the same for all the devices fabricated. The devices are passivated with MBE CdTe. Photodiodes have been characterized as a function of temperature. R₀A_imp values obtained between 300 and 78K are comparable for the two substrates and are approximately a factor of five below theoretical values calculated from measured material parameters. The data, for the PACE-1 substrate, indicates diffusion limited performance down to 110K. Area dependence gives further indications as to the origin of diffusion currents. Comparable R₀A_imp for various diode sizes indicates a p-side origin. R₀A and optical characteristics for the photodiodes grown on lattice-matched CdZnTe substrates and lattice mismatched PACE-1 are comparable. Howover, differences were observed in the noise characteristics of the photodiodes. Noise was measured on 50 × 50 μm devices held under a 100 mV reverse bias. At 110K, noise spectrum for devices from the two substrates is in the low 10⁻¹⁵ A/Hz^1/2 range. This value reflects the Johnson noise of the room temperature 10¹⁰ Ω feedback resistor in the current amplifier that limits the minimum measurable noise. Noise at 1 Hz, −100 mV and 120K for the 4.95 μm PACE-1 devices is in the 1–2 × 10⁻¹⁴ A/Hz^1/2, a factor of 5–10 lower than previously grown typical PACE-1 n⁺-on-p layers. Noise at 120K for the 4.60 μm PACE-1 and LPE on CdZnTe was again below the measurement technique limit. Greatest distinction in the noise characteristics for the different substrates was observed at 163K. No excess low frequency noise was observed for devices fabricated on layers grown by LPE on lattice-matched CdZnTe substrates. Photodiode noise measured at 1Hz, −100 mV and 163K in the 4.60 μm PACE-1 layer is in the 1–2×10⁻¹³ A/Hz^1/2, again a factor of 5–10 lower than previously grown PACE-1 n⁺-on-p layers. More variation in noise (4×10⁻¹³−2×10⁻¹² A/Hz^1/2) was observed for devices in the 4.95 μm PACE-1 layer. DLPH devices fabricated in HgCdTe layers grown by LPE on lattice-matched CdZnTe and on lattice-mismatched PACE-1 have comparable R₀A and quantum efficiency values. The distinguishing feature is that the noise is greater for devices fabricated in the layer grown on lattice mismatched substrates, suggesting dislocations inherent in lattice mismatched material affects excess low frequency noise but not zero bias impedance.     

Annealing effect on the P-type carrier concentration in low-temperature processed arsenic-doped HgCdTe

We report the results of annealing effects on the As-doped alloy HgCdTe grown by molecular beam epitaxy (MBE), arsenic (As) diffusion in HgCdTe from Hg-rich solutions at low temperatures, and As ion implantation at room temperature. Hall-effect measurements, secondary ion mass spectrometry and p-on-n test photodiodes were used to characterize the As activation. High As-doping levels (10¹⁷−10¹⁹ cm⁻³) could be obtained using either MBE growth, As diffusion or As ion-implantation. Annealed below 400°C, As doping in HgCdTe shows n-type characteristics, but above 410°C demonstrates that all methods of As doping exhibit p-type characteristics independent of As incorporation techniques. For example, for samples annealed at 436°C (P_Hg≈2 atm), in addition to p-type activation, we observe a significant improvement of p/n junction characteristics independent of the As source; i.e. As doping either in situ, by diffusion, or ion implantation. A study of this As activation of As-doped MBE HgCdTe as a function of anneal temperature reveals a striking similarity to results observed for As diffusion into HgCdTe and implanted As activation as a function of temperature. The observed dependence of As activation on partial pressure of Hg at various temperatures in the range of 250 to 450°C suggests that As acts as an acceptor at high Hg pressure (>1 atm) and as a donor at low Hg pressure (<1 atm) even under Hg-rich conditions.     

HgCdTe growth on (552) oriented CdZnTe by metalorganic vapor phase epitaxy

We report the growth of HgCdTe on (552)B CdZnTe by metalorganic vapor phase epitaxy (MOVPE). The (552) plane is obtained by 180 rotation of the (211) plane about the [111] twist axis. Both are 19.47 degrees from (111), but in opposite directions. HgCdTe grown on the (552)B-oriented CdZnTe has a growth rate similar to the (211)B, but the surface morphology is very different. The (552)B films exhibit no void defects, but do exhibit ∼40 μm size hillocks at densities of 10–50 cm⁻². The hillocks, however, are significantly flatter and shorter than those observed on (100) metalorganic vapor phase epitaxy (MOVPE) HgCdTe films. For a 12–14 μm thick film the height of the highest point on the hillock is less than 0.75 μm. No twinning was observed by back-reflection Laue x-ray diffraction for (552)B HgCdTe films and the x-ray double crystal rocking curve widths are comparable to those obtained on (211)B films grown side-by-side and with similar alloy composition. Etch pit density (EPD) measurements show EPD values in the range of (0.6–5)×10⁵ cm⁻², again very similar to those currently observed in (211)B MOVPE HgCdTe. The transport properties and ease of dopant incorporation and activation are all comparable to those obtained in (211)B HgCdTe. Mid-wave infrared (MWIR) photodiode detector arrays were fabricated on (552)B HgCdTe films grown in the P-n-N device configuration (upper case denotes layers with wider bandgaps). Radiometric characterization at T=120–160 K show that the detectors have classical spectral response with a cutoff wavelength of 5.22 μm at 120 K, quantum efficiency ∼78%, and diffusion current is the dominant dark current mechanism near zero bias voltage. Overall, the results suggest that (552)B may be the preferred orientation for MOVPE growth of HgCdTe on CdZnTe to achieve improved operability in focal plane arrays.     

Role of Dislocation Scattering on the Electron Mobility of n-Type Long Wave Length Infrared HgCdTe on Silicon

It has been reported that the basic electrical properties of n-type long wave length infrared (LWIR) HgCdTe grown on silicon, including the majority carrier mobility (μ _e) and minority carrier lifetime (τ), are qualitatively comparable to those reported for LWIR HgCdTe grown on bulk CdZnTe by molecular beam epitaxy (MBE). Detailed measurements of the majority carrier mobility have revealed important differences between the values measured for HgCdTe grown on bulk CdZnTe and those measured for HgCdTe grown on buffered silicon substrates. The mobility of LWIR HgCdTe grown on buffered silicon by MBE is reported over a large temperature range and is analyzed in terms of standard electron scattering mechanisms. The role of dislocation scattering is addressed for high dislocation density HgCdTe grown on lattice-mismatched silicon. Differences between the low temperature mobility data of HgCdTe grown on bulk CdZnTe and HgCdTe grown on silicon are partially explained in terms of the dislocation scattering contribution to the total mobility.     

Fabrication of high-performance large-format MWIR focal plane arrays from MBE-grown HgCdTe on 4″ silicon substrates

We have developed the capability to grow HgCdTe mid-wave infrared radiation double-layer heterojunctions (MWIR DLHJs) on 4″ Si wafers by molecular beam epitaxy (MBE), and fabricate devices from these wafers that are comparable to those produced by mature technologies. Test data show that the detectors, which range in cutoff wavelength over 4–7 μm, are comparable to the trendline performance of liquid phase epitaxy (LPE)-grown material. The spectral characteristics are similar, with a slight decrease in quantum efficiency attributable to the Si substrate. With respect to R₀A, the HgCdTe/Si devices are closer to the theoretical radiative-limit than LPE-grown detectors. Known defect densities in the material have been correlated to device performance through a simple model. Slight 1/f noise increases were measured in comparison to the LPE material, but the observed levels are not sufficient to significantly degrade focal plane array (FPA) performance. In addition to discrete detectors, two FPA formats were fabricated. 128×128 FPAs show MWIR sensitivity comparable to mature InSb technology, with pixel operability values in excess of 99%. A 640×480 FPA further demonstrates the high-sensitivity and high-operability capabilities of this material.     

Modeling of LWIR HgCdTe Auger-Suppressed Infrared Photodiodes under Nonequilibrium Operation

The general approach and effects of nonequilibrium operation of Auger-suppressed HgCdTe infrared photodiodes are well understood. However, the complex relationships of carrier generation and dependencies on nonuniform carrier profiles in the device prevent the development of simplistic analytical device models with acceptable accuracy. In this work, finite element methods are used to obtain self-consistent steady-state solutions of Poisson’s equation and the carrier continuity equations. Experimental current–voltage characteristics between 120 K and 300 K of HgCdTe Auger-suppressed photodiodes with cutoff wavelength of λ _c = 10 μm at 120 K are fitted using our numerical model. Based on this fitting, we study the lifetime in the absorber region, extract the current mechanisms limiting the dark current in these photodiodes, and discuss design and fabrication considerations in order to optimize future HgCdTe Auger-suppressed photodiodes.     

Midwave-infrared negative luminescence properties of HgCdTe devices on silicon substrates

We have investigated the negative luminescence properties of a midwave-infrared (MWIR) HgCdTe photodiode (λ_co = 5.3 μm at 295 K) grown on a silicon substrate. The internal negative luminescence efficiencies measured using a self-referencing optical technique were 88% throughout the 3–5 μm spectral region and nearly independent of temperature in the 240–300 K range. This corresponds to an apparent temperature reduction of 53 K at room temperature and 35 K at 240 K. Efficiencies measured by an electrical modulation technique were consistent with the measured internal efficiencies and the measured reflectivity of the device. This is the highest efficiency and largest apparent reduction in temperature reported to date, and slightly higher than that measured earlier for photodiodes grown on CdZnTe despite a longer cut-off wavelength. These results provide further indication that the HgCdTe/Si photovoltaic device technology is capable of combining high quality with high yield.