The minority carrier lifetime in doped and undoped p-type Hg0.78Cd0.22Te liquid phase epitaxy films

This paper will describe: (1) the first comparative study of recombination mechanisms between doped and undoped p-type Hg_1-xCd_xTe liquid phase epitaxy films with an x value of about 0.22, and (2) the first determination of τ_A7 ⁱ/τ_A1 ⁱ ratio by lifetime’s dependence on both carrier concentration and temperature. The doped films were either copper- or gold-doped with the carrier concentration ranging from 2 x 10¹⁵ to 1.5 x 10¹⁷ cm^-3, and the lifetime varied from 2 μs to 8 ns. The undoped (Hg-vacancy) films had a carrier concentration range between 3 x 10¹⁵ and 8 x 10¹⁶ cm^-3, and the lifetime changed from 150 to 3 ns. It was found that for the same carrier concentration, the doped films had lifetimes several times longer than those of the undoped films, limited mostly by Auger 7 and radiative recombination processes. The ineffectiveness of Shockley-Read-Hall (SRH) recombination process in the doped films was also demonstrated in lifetime vs temperature curves. The important ratio of intrinsic Auger 7 lifetime to intrinsic Auger 1 lifetime, τ_A7 ⁱ/τ_A1 ⁱ, was determined to be about 20 from fitting both concentration and temperature curves. The reduction of minority carrier lifetime in undoped films can be explained by an effective SRH recombination center associated with the Hg vacancy. Indeed, a donor-like SRH recombination center located at midgap (E_v+60 meV) with a capture cross section for minority carriers much larger than that for majority carriers was deduced from fitting lifetime vs temperature curves of undoped films.     

Performance limiting surface defects in SiC epitaxial p-n junctiondiodes

Effects of surface defects on performance of kV-class 4H- and 6H-SiC epitaxial p-n junction diodes were investigated. The perimeter recombination and generation, instead of the bulk process, are responsible for forward recombination current and reverse leakage current of the diodes, respectively. Mapping studies of surface morphological defects have revealed that triangular-shaped defects severely degrade high-blocking capability of the diodes whereas shallow round pits and scratch give no direct impact. Device-killing defects in SiC epilayers are discussed based on breakdown voltage mapping. Effective minority carrier lifetimes are mainly limited not by bulk recombination but by perimeter recombination     

Technological Features of Irradiation of Sip+-n-n+ Diodes with Electrons at Elevated Temperatures

The behavior of the lifetime of nonequilibrium charge carriers τ_p, the reverse current I _R, and the forward-voltage drop U _F in electron-irradiated (E _irr = 6 MeV) commercial p ⁺-n-n ⁺ diodes at irradiation temperatures in the range of T _irr = 20–400°C is studied. Studies have been performed for samples fabricated on a single-crystal Si substrate either doped with phosphorus in the course of growth by the Czochralski method (Cz-n-Si:P) or doped with phosphorus by nuclear transmutations, neutron-transmutation doped Si (NTD n-Si:P). It is shown that, by choosing the temperature conditions of technological irradiation, one can solve the problem of attaining small values of τ_p at a minimal increase in U _F and I _R in fast-response diodes. It is established that, in the case of comparable variations in τ_p in the base region of diodes, the best relation between U _F and I _R is observed at T _irr = 300°C in n-Si:P samples doped by the Czochralski method and at T _irr = 350°C in samples doped by reactions induced by thermal neutrons.     

Long hole spin relaxation times in diluted magnetic semiconductor heterostructures

We report the observation of long spin lifetimes for heavy holes in (Zn,Mn)Se and (Zn,Fe)Se based heterostructures. These long spin relaxation times are observed in both simple strained epilayers, as well as in complex spin superlattice structures in which the spin up and spin down carriers occupy alternating layers of the superlattice. In photoluminescence spectra, both the higher energy (+1/2, +3/2) and lower energy (−1/2, −3/2)heavy hole exciton interband transitions are observed, even though it would be energetically favorable for the spin up carriers to first relax to the spin down state before radiative recombination. From the magnetic field dependence of the intensity ratio of these components and a rate equation model, we find that the heavy hole spin lifetime τ_hs is substantially longer than the electron spin lifetime τ_es, with τ_hs /τ_r ≈ 4 and τ_es /τ_r ≈ 0.06, where τ_r is the radiative recombination time. This is attributed to the strain induced splitting of the heavy and light hole bands, which inhibits mixing of the hole spin states and subsequent dipole-allowed transitions producing fast spin relaxation.     

An evaluation of contamination from plasma immersion ion implantation on silicon device characteristics

Silicon devices including diodes, metal oxide semiconductor capacitors, and p-channel metal oxide semiconductor transistors were fabricated by plasma immersion ion implantation (PHI) doping technique using a microwave multipolar bucket plasma system. B₂H₆ diluted in helium (1%) was used as the gas source. The contamination by helium, hydrogen, iron, sodium, and aluminum impurities was evaluated by secondary ion mass spectrometry measurements. During PHI processing in an aluminum chamber with a stainless steel wafer holder, no aluminum and a dose of 4.1 x 10¹²/cm² of Fe were detected. Most of Fe ions were shielded by a thin layer of SiO₂ during the device fabrications. Good quality devices have been demonstrated including low reverse current of 15 nA/cm² (V_R = -5 V) in diodes and reasonable lifetimes of the minority carriers such as t_g = 55.0 μsec and = τ_r 54.2 μsec.     

Reverse recovery in p-n junction diodes with built-in drift fields

This paper extends the earlier analysis of Moll, Krakauer and Shen of the reverse recovery of a symmetrical p-n junction diode with built-in retarding drift field in the base to the diodes in which the effect of bulk recombinations in the base is important. It is shown that the effect of bulk recombination becomes important if $\text{J}{}_{\mathrm{f}}\text{J}{}_{\mathrm{R}}\text{? 0.5}$ (J_F and J_R are the forward and the reverse currents respectively) even when the drift field is very strong. For very strong retarding fields, t_s vs ln $\text{(1 +}\text{J}{}_{\mathrm{F}}\text{J}{}_{\mathrm{R}}\text{)}$ plot is linear and has a slope very close to the minority carrier lifetime τ_B in the base even for small values of time. Hence, τ_B can be conveniently determined by this method for such diodes. Expressions for the charge left in the base at the end of the storage phase and for the decay of the current in the second phase are also derived and discussed.     

Current transport in porous p-Si and Pd-porous Si structures

Mechanisms are investigated for current transport in porous p-Si and Pd-p-por-Si structures in the temperature range 78–300 K. It is shown that at 78 K drift transport is decisive, with the participation of deep traps with a concentration N _t≈1.3×10¹³ cm⁻³. At higher temperatures the diffusion mechanism takes over, with I∼exp(−qV/nkT) and n=10–20. Relaxation processes for the reverse current and photocurrent (ascending branch) have a delayed character (up to t⋍100 s) and are determined by the effect of traps at a depth E _t=0.80 eV. The temperature behavior of the photocurrent (without a bias) is connected with recombination at a level E _r=0.12 eV, and its value essentially depends on the contribution of the basal region of the diode structure. Fiz. Tekh. Poluprovodn. 32, 1073–1075 (September 1998)     

Carrier Lifetimes in Lightly-Doped <Emphasis Type="Italic">p</Emphasis>-Type 4H-SiC Epitaxial Layers Enhanced by Post-growth Processes and Surface Passivation

We investigated limiting factors of carrier lifetimes and their enhancement by post-growth processes in lightly-doped p-type 4H-SiC epitaxial layers (N _A ～ 2 × 10¹⁴ cm^?3). We focused on bulk recombination, surface recombination, and interface recombination at the epilayer/substrate, respectively. The carrier lifetime of 2.8 μs in an as-grown epilayer was improved to 10 μs by the combination of V_C-elimination processes and hydrogen annealing. By employing surface passivation with deposited SiO₂ followed by POCl₃ annealing, a long carrier lifetime of 16 μs was obtained in an oxidized epilayer. By investigating carrier lifetimes in a self-standing p-type epilayer, it was revealed that the interface recombination at the epilayer/substrate was smaller than the surface recombination on a bare surface. We found that the V_C-elimination process, hydrogen annealing, and surface passivation are all important for improving carrier lifetimes in lightly-doped p-type epilayers.     

Reverse recovery transient characteristic of PEDOT:PSS/n-Si hybrid organic-inorganic heterojunction

We study the junction behavior of poly (3,4-ethylenedioxythiophene):polystyrenesulphonate/n-Si hybrid organic/inorganic heterojunction by reverse recovery transient (RRT) characterization. RRT response for PEDOT:PSS/n-Si hybrid junction is reported for various n-Si doping concentration and forward bias current injection level. The presence of settling time of 8.3–23.5 μs in the RRT response in contradiction to Schottky junction model commonly assumed for PEDOT:PSS/n-Si hybrid structure. The decrease in the minority carrier lifetime from 126.8 μs to 39.5 μs with increased n-Si doping concentration, suggests that minority carriers are stored at n-Si side of the junction, which is consistent with a p⁺-n junction model for the hybrid structure. The minority carrier lifetime is found to depend on forward bias current injection level, attributed to trap-saturation effect of the recombination-centers at the PEDOT:PSS/n-Si junction. The DC-IV characteristics of the PEDOT:PSS/n-Si hybrid junction are also consistent with the notion of diffusion and trap assisted recombination dominated dark current. The diffusion dominated transport of PEDOT:PSS/n-Si leads to an ideal p⁺-n junction behavior that leverages on the good transport properties of Si. Our findings are important in the modeling and optimization of the characteristics of electronic devices based on the organic/Si hybrid junction.     

Electron beam-induced current investigation of GaN Schottky diode

In this article, we report the electron beam-induced current (EBIC) measurements in a GaN Schottky diode performed in the line-scan configuration. A theoretical model with an extended generation source was used to accurately extract some minority carrier transport properties of the unintentionally doped n-GaN layer. The minority hole diffusion length is found to increase from ∼0.35 μm near the junction to ∼1.74 μm at the bulk regions. This change is attributed to an increase of the carrier lifetime caused by the polarization effects, which are preponderant in this component. For depth distances exceeding 0.65 μm, it is shown that the measured current is produced by the reabsorption recombination radiation process. This corresponds to an absorption coefficient of 0.178 μm⁻¹, in good agreement with the optical absorption measurement.     

Minority carrier lifetime in indium-doped HgCdTe(211)B epitaxial layers grown by molecular beam epitaxy

We have studied the minority-carrier lifetime on intentionally indium-doped (211)B molecular beam epitaxially grown Hg_1-xCd_xTe epilayers down to 80K with x ≈ 23.0% ± 2.0%. Measured lifetimes were explained by an Auger-limited band-to-band recombination process in this material even in the extrinsic temperature region. Layers show excellent electron mobilities as high as ≈2 x 10⁵ cm²v^-1s^-1 at low temperatures. When the layers are compensated with Hg vacancies, results show that the Schockley-Read recombination process becomes important in addition to the band-to-band processes. From the values of τ_n0 and τ_p0 of one sample, the obtained defect level is acceptor-like and is somewhat related to the Hg vacancies.     

Monte Carlo Modeling of VLWIR HgCdTe Interdigitated Pixel Response

Increasing very long-wave infrared (VLWIR, λ _c ≈ 15 μm) pixel operability was approached by subdividing each pixel into four interdigitated subpixels. High response is maintained across the pixel, even if one or two interdigitated subpixels are deselected (turned off), because interdigitation provides that the preponderance of minority carriers photogenerated in the pixel are collected by the selected subpixels. Monte Carlo modeling of the photoresponse of the interdigitated subpixel simulates minority-carrier diffusion from carrier creation to recombination. Each carrier generated at an appropriately weighted random location is assigned an exponentially distributed random lifetime τ _i, where 〈τ _i〉 is the bulk minority-carrier lifetime. The minority carrier is allowed to diffuse for a short time dτ, and the fate of the carrier is decided from its present position and the boundary conditions, i.e., whether the carrier is absorbed in a junction, recombined at a surface, reflected from a surface, or recombined in the bulk because it lived for its designated lifetime. If nothing happens, the process is then repeated until one of the boundary conditions is attained. The next step is to go on to the next carrier and repeat the procedure for all the launches of minority carriers. For each minority carrier launched, the original location and boundary condition at fatality are recorded. An example of the results from Monte Carlo modeling is that, for a 20-μm diffusion length, the calculated quantum efficiency (QE) changed from 85% with no subpixels deselected, to 78% with one subpixel deselected, 67% with two subpixels deselected, and 48% with three subpixels deselected. Demonstration of the interdigitated pixel concept and verification of the Monte Carlo modeling utilized λ _c(60 K) ≈ 15 μm HgCdTe pixels in a 96 × 96 array format. The measured collection efficiency for one, two, and three subelements selected, divided by the collection efficiency for all four subelements selected, matched that calculated using Monte Carlo modeling.     

Quantum spin Hall effect in nanostructures based on cadmium fluoride

Tunneling current-voltage (I-V) characteristics and temperature dependences of static magnetic susceptibility and specific heat of the CdB _x F_{2 − x} /p-CdF₂-QW/CdB _x F_{2 − x} planar sandwich structures formed on the surface of an n-CdF₂ crystal have been studied in order to identify superconducting properties of the CdB _x F_{2 − x} δ barriers confining the p-type CdF₂ ultranarrow quantum well. Comparative analysis of current-voltage (I-V) characteristics and conductance-voltage dependences (measured at the temperatures, respectively, below and above the critical temperature of superconducting transition) indicates that there is an interrelation between quantization of supercurrent and dimensional quantization of holes in the p-CdF₂ ultranarrow quantum well. It is noteworthy that detection of the Josephson peak of current in each hole subband is accompanied by the appearance of the spectrum of the multiple Andreev reflection (MAR). A high degree of spin polarization of holes in the edge channels along the perimeter of the p-CdF₂ ultranarrow quantum well appears as a result of MAR and makes it possible to identify the quantum spin Hall effect I-V characteristics; this effect becomes pronounced in the case of detection of nonzero conductance at the zero voltage applied to the vertical gate in the Hall geometry of the experiment. Within the energy range of superconducting gap, the I-V characteristics of the spin transistor and quantum spin Hall effect are controlled by the MAR spectrum appearing as the voltage applied to the vertical gate is varied. Beyond the range of the superconducting gap, the observed I-V characteristic of the quantum spin Hall effect is represented by a quantum conductance staircase with a height of the steps equal to e ₂/h; this height is interrelated with the Aharonov-Casher oscillations of longitudinal and depends on the voltage applied to the vertical gate.     

High-low junctions for solar cell applications

A new theoretical model to calculate the effective surface recombination velocity (S_eff) of a high-low junction with an arbitrary impurity distribution is presented. The model is applied to erfc-diffused pp⁺ junctions using experimental data of bandgap narrowing, lifetime and mobility. Bandgap narrowing is shown to degrade the minority carrier reflecting properties of the high-low junction. Computer results are applied for the design of BSF solar cells and to study other solar cells structures based on high-low junctions.     

Temperature dependence of minority hole mobility in n+-GaAs measured with a new variable temperature technique

The temperature-dependent mobility provides essential information for device design and serves as a sensitive probe of minority carrier scattering physics. As examples, dominant scattering mechanisms are identified by characteristic temperature dependencies of mobility and for low temperature bipolar device optimization, accurate minority carrier mobility data are required. We report the first temperature (T) dependent measurement of minority hole mobility in n⁺-GaAs. The minority carrier mobility (μ) was measured with the zero-field time-of-flight technique. In this technique, minority carrier diffusivity (D), where De = μkT, is determined from the transient response of a specially designed photodiode that is excited by a high-speed laser. We have extended the technique to permit continuously variable, T-dependent minority mobility measurements. The unique cryostat design, including device mounting, low-loss feedthroughs and temperature measurement scheme, is presented.     

Modeling silicon emitters for VLSI transistors

The accuracy and reliability of predictions from numerical simulations of advanced bipolar transistors for VLSI applications depend on model input parameters. These parameters include the variations with doping and carrier concentrations in both n-type and p-type silicon of (1) the valance and conduction band edges, (2) the effective intrinsic carrier concentrations, (3) the minority carrier mobilities, and (4) the minority carrier lifetimes. This paper reviews recent advances in device physics for modeling the emitters of bipolar transistors with submicrometer dimensions and high concentrations of dopant ions and carriers.     

Interfacial dipole in organic p–n junction to realize write-once–read-many-times memory

A new approach is exploited to realize nonvolatile organic write-once–read-many-times (WORM) memory based on copper phthalocyanine (CuPc)/hexadecafluoro-copper-phthalocyanine (F₁₆CuPc) p–n junction. The as-fabricated device is found to be at its ON state and can be programmed irreversibly to the OFF state by applying a negative bias. The WORM device exhibits a high ON/OFF current ratio of up to 2.6 × 10⁴. An interfacial dipole layer is testified to be formed and destructed at the p–n junction interface for the ON and OFF states, respectively. The ON state at positive voltage region is attributed to the efficient hole and electron injection from the respective electrodes and then recombination at the CuPc/F₁₆CuPc interface, and the transition of the device to the OFF state results from the destruction of the interfacial dipole layer and formation of an insulating layer which restricts charge carrier recombination at the interface.     

Analysis of perimeter recombination in the subcells of GaInP/GaAs/Ge triple‐junction solar cells

This paper studies the recombination at the perimeter in the subcells that constitute a GaInP/GaAs/Ge lattice‐matched triple‐junction solar cell. For that, diodes of different sizes and consequently different perimeter/area ratios have been manufactured in single‐junction solar cells resembling the subcells in a triple‐junction solar cell. It has been found that neither in GaInP nor in Ge solar cells the recombination at the perimeter is significant in devices as small as 500 μm × 500μm(2.5 ⋅ 10 ^{− 3} cm²) in GaInP and 250μm × 250μm (6.25 ⋅ 10 ^{− 4}cm²) in Ge. However, in GaAs, the recombination at the perimeter is not negligible at low voltages even in devices as large as 1cm², and it is the main limiting recombination factor in the open circuit voltage even at high concentrations in solar cells of 250 μm × 250μm (6.25 ⋅ 10 ^{− 4} cm²) or smaller. Therefore, the recombination at the perimeter in GaAs should be taken into account when optimizing triple‐junction solar cells. Copyright © 2014 John Wiley & Sons, Ltd.     

Diode and MOSFET Properties of Trench‐Gate‐Type Super‐Barrier Rectifier with P‐Body Implantation Condition for Power System Application

In this paper, we investigate the electrical characteristics of two trench‐gate‐type super‐barrier rectifiers (TSBRs) under different p‐body implantation conditions (low and high). Also, design considerations for the TSBRs are discussed in this paper. The TSBRs’ electrical properties depend strongly on their respective p‐body implantation conditions. In the case of the TSBR with a low p‐body implantation condition, it exhibits MOSFET‐like properties, such as a low forward voltage (V_F) drop, high reverse leakage current, and a low peak reverse recovery current owing to a majority carrier operation. However, in the case of the TSBR with a high p‐body implantation condition, it exhibits pn junction diode–like properties, such as a high V_F, low reverse leakage current, and high peak reverse recovery current owing to a minority carrier operation. As a result, the TSBR with a low p‐body implantation condition is capable of operating as a MOSFET, and the TSBR with a high p‐body implantation condition is capable of operating as either a pn junction diode or a MOSFET, but not both at the same time.