Doping level and type of GaInP saturable absorbing layers forrealizing pulsating 650-nm-band AlGaInP laser diodes

On AlGaInP laser diodes, the doping level and type of GaInP saturable absorbing (SA) layers suitable for self sustained pulsation are clarified. Optical properties of n- and p-type GaInP quantum wells (QWs) have been evaluated by means of time-resolved photoluminescence (TRPL) spectroscopy. As the doping level becomes higher, the recombination lifetime becomes shorter, and it can be reduced to 1.1 ns at our highest doping level (1=2×10¹⁸ cm^-3). For highly doped n-type QW, a PL peak energy shift as large as 26 meV is observed by high-density excitation. Highly doped p-type SA layer is suitable for self-sustained pulsating laser diodes, because it offers short recombination lifetime and no Burstein shift under highly excited condition     

Si/Si1-xGex heterojunction bipolartransistors produced by limited reaction processing

Si/Si_1-xGe_x heterojunction transistors (HBTs) fabricated by a chemical vapor deposition (CVD) technique are reported. A rapid thermal CVD limited-reaction processing (LRP) technique was used for the in situ growth of all three device layers, including a 20-mm Si_1-xGe_x layer in the base. The highest current gains observed (β=400) were for a Si/Si_1-x Ge_x HBT with a base doping of 7×10¹⁸ cm^-3 near the junction and a shallow arsenic implant to form ohmic contacts and increase current gain. Ideal base currents were observed for over six decades of current and the collector current remained ideal for nearly nine current decades starting at 1 pA. The bandgap difference between a p-type Si layer doped to 5×10¹⁷ cm^-3 and the Si_1-xGe_x(x=0.31) base measured 0.27 eV. This value was deduced from the measurements of the temperature dependence of the base current and is in good agreement with published calculations for strained Si_1-xGe_x layers on Si     

A novel fabrication technique for multiple-wavelengthphotonic-integrated devices in InGaAs-InGaAsP laserheterostructures

We report the fabrication of multiple wavelength chips in InGaAs-InGaAsP laser structure using a novel ion implantation induced quantum-well (QW) intermixing technique. This technique first consists of using a gray mask photolithography and reactive ion etching process to create a SiO₂ implant mask with variable thickness on the sample. This is followed by a single 360-keV phosphorus ion implantation at a dose of 1×10¹⁴ cm^-2 at 200°C, which creates different amounts of point defects in the sample depending on the local thickness of the SiO₂ mask. A subsequent thermal annealing step induces QW intermixing through the diffusion of the point defects across the structure. With this technique, we have successfully fabricated 10-channel multiple wavelength laser diodes, with lasing wavelength spreading over 85 nm (between 1.47 and 1.55 μm), monolithically integrated on a single chip. Only a limited increase of threshold current density of 17% (i.e., from 1.2 to 1.4 kA/cm²), has been observed between the least intermixed and the most intermixed lasers     

Bulk and surface properties of amorphous hydrogenated fluorinatedsilicon grown from SiF4 and H2

A detailed study of the growth of amorphous hydrogenated fluorinated silicon (a-Si:H, F) from a DC glow discharge in SiF₄ and H₂ is discussed. The electrical properties of the films can be varied over a very wide range. The bulk properties of the best films that were measured included an Urbach energy E_u =43 meV, a deep-level defect density N_s=1.5×10¹⁵ cm^-3, and a hole drift mobility of 8×10^-3 cm² V^-1 s^-1, which reflects a characteristic valence band energy of 36 meV. It was found that E_u, N _s, and the density of surface states N_ss are related to each other. Under the deposition condition of the films with the best bulk properties, N_ss reaches its highest value of 1×10¹⁴ cm^-2. It is suggested that in growth from SiF₄/H₂, the density of dangling bonds at the growing surface is very sensitive to the deposition conditions     

InGaAsPN-InP-based photodetectors for long wavelength(λ>1.65 μm) applications

We demonstrate InGaAsPN p-i-n photodetectors lattice-matched to InP substrates with cutoff wavelengths larger than 1.65 μm. The narrow bandgap InGaAsPN absorption layers were grown by gas source molecular beam epitaxy using an RF plasma nitrogen source. Optical absorption spectra reveal that InGaAsPN with 5% P and 2.8% N has a cutoff wavelength λ_CO=1.90 μm Background doping in the absorption layer for a detector with 1.5% N and 5% P is reduced from (1.5±0.5)×10¹⁷ cm^-3 for the as-grown device, to (5±0.5)×10¹⁶ cm^-3 for a thermally annealed device. The unintentional high background doping is due to N-H bond formation or local strain induced defects. Spectral response measurements indicate that λ_CO=1.85 μm is achieved for detectors annealed at 800°C with 2% N and 5% P in the InGaAsPN absorption layer, suggesting that annealed InGaAsPN alloys are promising for use in detectors with response in the near and mid-IR wavelength spectral range     

Carrier transport related analysis of high-power AlGaN/GaN HEMTstructures

Shubnikov-de Haas (SdH) oscillation and Hall measurement results were compared with HEMT DC and RF characteristics for two different MOCVD grown AlGaN-GaN HEMT structures on semiinsulating 4H-SiC substrates. A HEMT with a 40-nm, highly doped AlGaN cap layer exhibited an electron mobility of 1500 cm²/V/s and a sheet concentration of 9×10¹² cm at 300 K (7900 cm²/V/s and 8×10¹² cm^-2 at 80 K), but showed a high threshold voltage and high DC output conductance. A 27-nm AlGaN cap with a thinner, lightly doped donor layer yielded similar Hall values, but lower threshold voltage and output conductance and demonstrated a high CW power density of 6.9 W/mm at 10 GHz. The 2DEG of this improved structure had a sheet concentration of n_SdH=7.8×10¹² cm^-2 and a high quantum scattering lifetime of τ_q=1.5×10^-13 s at 4.2 K compared to n_SdH=8.24×10¹² cm^-2 and τ_q=1.72×10^-13 s for the thick AlGaN cap layer structure, Despite the excellent characteristics of the films, the SdH oscillations still indicate a slight parallel conduction and a weak localization of electrons. These results indicate that good channel quality and high sheet carrier density are not the only HEMT attributes required for good transistor performance     

Minority-carrier transport parameters in heavily doped p-typesilicon at 296 and 77 K

Minority-carrier electron lifetime, mobility and diffusion length in heavily doped p-type Si were measured at 296 and 77 K. It was found that a 296 K μ_n (pSi)≈μ_n (nSi) for N _AA≲5×10¹⁸ cm^-3, while μ_n (pSi)/μ_n (nSi)≈1 to 2.7 for higher dopings. The results also show that for N_AA≲3×10¹⁹ cm^-3, D (pSi) at 77 K is smaller than that at 296 K, while for higher dopings D_n (pSi) is larger at 77 K than at 296 K. μ_n (pSi) at 77 K increases with the increasing doping above N_AA>3×10¹⁸ cm^-3, in contrast to the opposite dependence for μ_n (nSi) in n⁺ Si     

KrF excimer laser annealed TFT with very high field-effect mobilityof 329 cm2/V-s

A thin-film transistor (TFT) with a maximum field-effect mobility of 320 cm²/V-s, an on/off current ratio of 7.6×10⁷ , a threshold voltage of 6.7 V and a subthreshold slope of 0.37 V/decade was fabricated by using pulse laser annealing processes. Amorphous silicon films (a-Si:H) with a very low impurity concentration of 4×10¹⁸ cm^-3 for oxygen, 1.5×10¹⁸ cm^-3 for carbon, and 2×10¹⁷ cm^-3 for nitrogen were deposited by a plasma chemical vapor deposition (CVD) method and annealed by KrF excimer laser (wavelength of 248 nm). The Raman spectroscopy technique was a useful tool for optimizing laser annealing conditions. Experimental results show that two factors are very important for fabricating very-high mobility TFTs: (1) utilizing high-purity as-deposited a-Si:H film; and (2) performing whole laser annealing processes sequentially in a vacuum container and optimizing illumination conditions     

Deep-level dominated current-voltage characteristics of buriedimplanted oxide silicon-on-insulator

Current-voltage characteristics of Au contacts formed on buried implanted oxide silicon-on-insulator (SOI) structures are discussed, which indicate that the dominant transport mechanism is space-charge-limited current (SCLC) conduction in the presence of deep-level states. The deep-level parameters, determined using a simple analysis, appear to be sensitive to anneal conditions used and subsequent processing. Silicon implanted with 1.7×10¹⁸ cm^-2 oxygen ions at 150 keV following a 1200°C anneal for 3 h shows deep level 0.37 eV below the conduction band edge with a concentration of unoccupied traps of ~ 2×10¹⁵ cm^-3 . In contrast, arsenic ion implantation, in the 1200°C annealed material with a dose of 1.5×10¹² cm^-2 at 60 keV and activated by rapid thermal annealing (RTA), introduces a deep level 0.25 eV below the conduction band edge with an unoccupied trap concentration of ~6×10¹⁷ cm^-2     

Studies of diffused boron emitters: saturation current, bandgapnarrowing, and surface recombination velocity

The emitter saturation current density, J₀ was measured on diffused boron emitters in silicon for the case in which the emitter surface is passivated by a thermal oxide and for the case in which Al/Si is deposited on the emitter surface. The oxide-passivated emitters have a surface recombination velocity, s, which is near its lowest technologically achievable value. In contrast, the emitters with Al/Si on the surface have surface recombination velocities which approach the maximum possible value of s. From the J ₀ measurements, the apparent bandgap narrowing as a function of boron doping was found. Using this bandgap narrowing data, the surface recombination velocity at the Si/SiO₂ interface was extracted for surface boron concentrations from 3×10¹⁷ to 3×10¹⁹ cm^-3     

Linewidth enhancement factor in strained quantum well lasers

The linewidth enhancement factor α of strained quantum-well lasers is analyzed by the k-p perturbation method using the effective-mass approximation. It is found that the α factor in a strained In_0.80Ga_0.20As/InP quantum-well (QW) laser with 1.9% biaxial compression is less than 1.5. For a strained QW laser with p-type modulation doping (MD) of 5×10 ¹⁸ cm^-3, the α factor is as small as 0.8. It is also demonstrated that the spectral linewidth and wavelength chirping in the strained MD QW laser are significantly less than those in conventional bulk and QW lasers     

A semi-empirical model for the field-effect mobility ofhydrogenated polycrystalline-silicon MOSFETs

The quantitative relationship between field-effect mobility (μ _FE) and grain-boundary trap-state density (N_t ) in hydrogenated polycrystalline-silicon (poly-Si) MOSFETs is investigated. The focus is on the field-effect mobility in MOSFETs with N_t 1×10² cm^-2. It is found that reducing N_t to as low as 5×10¹¹ cm^-2 has a great impact on μ_FE. MOSFETs with the N_t of 4.2×10¹¹ cm^-2 show an electron mobility of 185 cm²/V-s, despite a mean grain size of 0.5 μm. The three principal factors that determine μ_FE, namely, the low-field mobility, the mobility degradation factor, and the trap-state density N_t are clarified     

4H-SiC MOSFETs utilizing the H2 surface cleaningtechnique

The H₂ cleaning technique was examined as the precleaning of the gate oxidation for 4H-SiC MOSFETs. The device had a channel width and length of 150 and 100 μm, fabricated on the p-type epitaxial layer of 3×10¹⁶ cm^-3. The gate oxidation was performed after the conventional RCA cleaning, and H₂ annealing at 1000°C. The obtained channel mobility depends on the pre-cleaning process strongly, and was achieved 20 cm²/N s in the H₂ annealed sample. The effective interface-state density was also measured by the MOS capacitors fabricated on the same chips, resulting 1.8×10¹² cm^-2 from the photo-induced C-V method     

Measurements and modeling of MOSFET I-V characteristics withpolysilicon depletion effect

The authors study the degradation of MOSFET current-voltage (V-I) characteristics as a function of polysilicon gate concentration (N_p ), oxide thickness (t_ox) and substrate impurity concentration (N_D) using measured and modeled results. Experimentally it is found that for MOSFETs with thin gate oxide (t_ox≈70 Å) and high substrate concentration (N_D ≈1.6×10¹⁷ cm^-3) the reduction in the drain current I_DS can be as large as 10% to 20% for devices with insufficiently doped polysilicon gate (5×10¹⁸ ⩽N_p⩽1.6×10¹⁹ cm^-3). Theoretically it is shown that the drain current degradation becomes more pronounced as N_p decreases, t_ox decreases, or N_D, increases. A modified Pao-Sah model that takes into account the polysilicon depletion effect and an accurate gate-field-dependent mobility model are used to compute I-V characteristics for various values of N_p, t_ox, and N_D. Good agreement between experimental and modeled results is observed over a wide range of devices     

Molecular beam epitaxial GaAs/AlGaAs heterojunction bipolartransistors on (311)A GaAs substrates with all-silicon doping

The authors have investigated the characteristics and reproducibility of Si-doped p-type (311)A GaAs layers for application to heterojunction bipolar transistors (HBTs) grown by molecular beam epitaxy (MBE). The authors obtained p=2.2×10¹⁹ cm^-3 in a layer grown at 670°C. They have used all-Si doping to grow n-p-n transistors. These devices exhibit excellent DC characteristics with β=230 in a device with base doping of p=4×10¹⁸ cm^-3     

Single-mode laser diode at 778-nm wavelength: effect of p-doping

An AlGaAs-GaAs double quantum well structure has been grown by metal-organic chemical vapor deposition. High p-doping of the cladding layer (4×10¹⁸ cm^-3) is used to optimize the performance of ridge waveguide laser diodes. A stable single-mode operation is obtained with output power of 120 mW at room temperature. The temperature constant T₀ is ~230 K. Improvements are explained by reduction of electron leakage and by the current self-distribution effect     

Reduction of oxide charge and interface-trap density in MOScapacitors with ITO gates

The electrical properties of MOS capacitors with an indium tin oxide (ITO) gate are studied in terms of the number density of the fixed oxide charge and of the interface traps N_f and N _it, respectively. Both depend on the deposition conditions of ITO and the subsequent annealing procedures. The fixed oxide charge and the interface-trap density are minimized by depositing at a substrate temperature of 240°C at low power conditions and in an oxygen-rich ambient. Under these conditions, as-deposited ITO films are electrically conductive. The most effective annealing procedure consists of a two-step anneal: a 45-s rapid thermal anneal at 950°C in N₂, followed by a 30 min anneal in N₂/20% H₂ at 450°C. Typical values obtained for N_it and N_f are 4.2×10¹⁰ cm^-2 and 2.8×10¹⁰ cm^-2, respectively. These values are further reduced to 1.9×10¹⁰ cm^-2 and ≲5×10⁹ cm^-2, respectively, by depositing approximately 25 nm polycrystalline silicon on the gate insulation prior to the deposition of ITO     

Effect of exponentially graded base doping on the performance ofGaAs/AlGaAs heterojunction bipolar transistors

The authors have fabricated n-p-n GaAs/AlGaAs heterojunction bipolar transistors (HBTs) with base doping graded exponentially from 5×10¹⁹ cm^-3 at the emitter edge to 5×10¹⁸ cm^-3 at the collector edge. The built-in field due to the exponentially graded doping profile significantly reduces base transit time, despite bandgap narrowing associated with high base doping. Compared to devices with the same base thickness and uniform base doping of 1×10¹⁹ cm^-3 , the cutoff frequency is increased from 22 to 31 GHz and maximum frequency of oscillation is increased from 40 to 58 GHz. Exponentially graded base doping also results ill consistently higher common-emitter current gain than uniform base doping, even though the Gummel number is twice as high and the base resistance is reduced by 40%     

Electrical properties of Si p+-n junctions for sub-0.25μm CMOS fabricated by Ga FIB implantation

p⁺-n junction diodes for sub-0.25-μm CMOS circuits were fabricated using focused ion beam (FIB) Ga implantation into n-Si (100) substrates with background doping of N_b=(5-10)×10 ¹⁵ and N_b⁺=(1-10)×10¹⁷ cm^-3. Implant energy was varied from 2 to 50 keV at doses ranging from 1×10¹³ to 1×10¹⁵ cm^-2 with different scan speeds. Rapid thermal annealing (RTA) was performed at either 600 °C or 700°C for 30 s. Diodes fabricated on N_b⁺ with 10-keV Ga⁺ exhibited a leakage current (^I_R) 100× smaller than those fabricated with 50-keV Ga⁺. Tunneling was determined to be the major current transport mechanism for the diodes fabricated on N_b⁺ substrates. An optimal condition for I_R on N_b⁺ substrates was obtained at 15 keV/1×10¹⁵ cm^-2. Diodes annealed at 600°C were found to have an I_R 1000× smaller than those annealed at 700°C. I-V characteristics of diodes fabricated on N_b substrates with low-energy Ga⁺ showed no implant energy dependence. I-V characteristics were also measured as a function of temperature from 25 to 200°C. For diodes implanted with 15-keV Ga ⁺, the cross-over temperatures between I_diff and I_g-r occurred at 106°C for N_b ⁺ and at 91°C for N_b substrates     

Fabrication of p-i-n photodiodes on LPE-grown substrates

Epitaxial growth of a thick heavily doped silicon layer on a highly resistive silicon wafer by the yo-yo solute feeding method and its application to p-i-n photodiodes are discussed. An abrupt transition of the impurity profile is obtained between the n⁺ layer (1.95×10¹⁹ cm^-3, 450 μm) and the n^- layer (7.0×10¹¹ cm^-3, 80 μm). It is possible to use the thick intrinsic layers as the active region of power devices