The recent development of p-GaAs homojunction interfacial workfunction internal photoemission (HIWIP) far-infrared (> 40 micrometers ) detectors for space application is reported. The emphasis is placed on the detector performance, which includes responsivity, quantum efficiency, bias effects, cutoff wavelength, uniformity, crosstalk, and noise. The results are promising and show that p-GaAs HIWIP detectors have high potential to become a strong competitor in far- infrared space applications.

The carrier lifetimes in In_xGa_1-xAs (InGaAs) ternary alloys for radiative and Auger recombination are calculated for temperature 300 K in the short wavelength range 1.5 < (lambda) < 3.7 micrometers . Due to photon recycling, an order of magnitude enhancements in the radiative lifetimes over those obtained from the standard van Roosbroeck and Shockley expression, has been assumed. The possible Auger recombination mechanisms (CHCC, CHLH and CHSH processes) in direct-gap semiconductors are investigated. In n-type and p-type materials the carrier lifetimes are similar. It is clearly shown that in the range of low doping concentration, the carrier lifetime is determined by radiative recombination. For n-type material in the range of higher doping level, a competition between radiative and CHCC processes take place; instead for p-type materials the most effective channel of Auger mechanisms is the CHSH process. A special attention has been put on discussion of the carrier lifetimes in both types of In_0.53Ga_0.47As materials. Consequence of enhancement in the radiative lifetime leads to higher ultimate performance of photodiodes. The performance (R_oA product) of heterostructure InGaAs photovoltaic devices are analyzed. Both the n-on-p (with p-type active region) as well as p-on- n (with n-type active region) are considered. Finally, theoretically predicted performance of InGaAs photodiodes are compared with experimental data reported by other authors.

Carrier transport mechanisms in photodiodes from narrow-gap HgCdTe and PbSnTe semiconductors for long wavelength infra- red and medium wavelength infra-red applications are discussed in connection with their use in hybrid multielement arrays for T approximately equals 77 - 150 K temperature range. It is shown that the bulk diffusion and thermal generation-recombination (GR) currents in depletion region determine carrier transport mechanisms in these photodiodes at zero bias. The transport mechanisms are changed for reverse-biased voltages at which diodes are operating with silicon read-out devices in hybrid arrays. In this case the dark current is determined not only by the GR recombination (Schockley-Read-Hall (SRH) recombination) via the centers in the gap, but preferentially by two non-thermal mechanisms: (1) interband tunneling via the traps in the gap, and (2) direct band-to-band tunneling. The last one is important only at rather high electron concentrations n >= 10¹⁶ cm^-3 or n >= 2(DOT)10¹⁸ cm^-3 in HgCdTe and PbSnTe photodiodes, respectively and at large reverse-bias (V >= 0.2 V) voltages. The parameters of the traps (density of states, energy level position, capture cross section) have been estimated from the fit of calculated transport characteristics to the measured dependences on bias and temperature in the photodiodes of both investigated compounds. One level of traps in the gap for SRH recombination and trap-assisted tunneling mechanisms were used in fitting procedure. The best fit was obtained for the model in which the level of the traps was near the middle or slightly shifted from the middle of the gap towards the conduction band edge.

Narrow gap intrinsic semiconductors, extrinsic semiconductors and low dimensional structures have been used for infrared applications. Here we propose indium antimonide for infrared photodetectors operating in the 3 - 5 micrometers wavelength range at 80 K. These high performance single or multi-element detectors are typically fabricated from bulk InSb, using processes in involving the diffusion of dopants to product the p⁺-n homojunctions. We present a new growth technique, RF magnetron sputter epitaxy, where indium and antimony are supplied from solid n-InSb sputter target. Using this technique we have deposited n⁺-type epilayers on p-type bulk InSb A 1 - 2 micrometers n⁺ InSb layer grown on p InSb at a growth temperature of 350 - 370 degree(s)C. The layers show excellent surface morphology and crystallinity. We have used these epilayers to fabricate homojunction infrared photodiodes. The spectral and I-V characteristics of this diode have been presented and compared with the more widely reported metallurgical diffused junctions. This is the first material quality obtained for InSb nucleated directly onto InSb by rf magnetron sputter epitaxy simultaneously formatting np junction reported to date.

Carrier lifetimes in Hg_1-xCd_xTe (x equals 0.195 - 0.230) structures grown by molecular beam epitaxy are presented. The carrier lifetimes have been determined from photoconductivity decay after excitation with radiation pulse at various wavelength. It is clearly shown that borders of epitaxial layers influence their photoelectrical properties.

The influence of thermal annealing on electrical properties of p-n structures formed by ion beam milling (IBM) on vacancy doped Cd_xHg_1-xTe (x equals 0.205) single crystals with p (77 K) equals 5.8(DOT)10¹⁵ cm^-3 was investigated. After IBM of the initial samples the n-type layers were created with the thickness about 10 (mu) and electron concentration of the main part of n-type layers 5(DOT)10¹⁴ cm^-3. P-n structures were annealed in air at 85, 120 and 160 degree(s)C during 1, 2, and 4 hours. Degradation of the p-n structure after every annealing step was estimated on changes of the Hall coefficient dependence of magnetic field. It was revealed that degradation of the p-n structure took place due to progressive thickness decreasing of n-layer through Hg passing to intersites and vacancy creation. The critical temperature during technology steps is equal about 100 degree(s)C.

Experimental investigations of (Cd,Hg)Te have been performed with the use of ns- and ms-duration pulses of solid state laser. Changes in the chemical composition of the irradiated surface have been analyzed by means of X-ray photoelectron and Auger electron spectroscopies. Single crystalline HgTe and (Cd,Hg)Te wafers and epitaxial films have been used as the experimental samples. Processes of integral evaporation with generation of a molten zone with thickness up to several micrometers dominate upon ns-pulses irradiation and crystallization follows autoepitaxy laws. There was not observed increase of linear defects density in the layer near surface. Inverse layer depth in n-(Cd,Hg)Te coincides with molten zone. In the case of ms-pulses the influenced zone is several tenth micrometers thick. Irradiation of the samples at T equals 500 - 600 K in saturated Hg vapor completely suppresses the change of the surface composition. Heating of (Cd,Hg)Te sample leads to generation of a great number of acceptor-type native defects. As a results p-n junctions are formed in n-(Cd,Hg)Te by pulsed laser irradiation.

Results of complex investigations of n- and p-type Hg_1-xCd_xTe (MCT) etching in RF mercury glow discharge have been presented. Discharge was induced in quasi-closed volume. Results of technology parameter influence onto velocity of etching have been presented. It has been shown that MCT treatment by mercury ions can be carried out with etching velocity up to 30 micrometers /hour. Surface heating under these conditions slightly increases the temperature (up to 50 degree(s)C) and stoichiometry deviations are absent. It has been found that the width of disturbed layer depends on bias voltage and is smaller than 2.5 micrometers . Electrophysical parameters of n- and p-type MCT after processing have been studied. Etching of n-MCT forms the n⁺-n structure. The width of n⁺-layer corresponds to the width of disturbed zone. In the case of p-MCT, there exists inversion of conductivity type at depths exceeding those corresponding to the case of argon ions etching. It is supposed that high inversion velocity is caused by saturation of MCT surface by mercury ions during treatment.

Influence of interfacial recombination of charge carriers on photoconductivity of graded-band-gap semiconductor structures with extrinsic type of a conductivity and linear spatial dependence of band-gap is investigated theoretically. Effects of illumination of the structures from wide band gap side by strongly absorbed monochromatic light and by polychromatic light which uniformly generates photocarriers in the sample have been analyzed. Spectral dependences of the photoconductivity of the graded-band-gap semiconductor structures illuminated by monochromatic light are shown to have pronounced minimum occurring at photon energy equal to band-gap energy at the interface. Under conditions of coordinate-independent photocarrier generation rate the influence of interfacial recombination on the graded-band-gap semiconductor structure photosensitivity displays most substantially in the case when the sample thickness is of the order of minority carrier diffusion length.

Gate-controlled diodes were made by using evaporated indium electrodes overlapping the edge of mesa diodes, isolated from the surface by a layer of ZnS or by native anodic oxide of InSb or HgCdTe. The resulting 3D device characteristics with gate voltage as a parameter have been investigated. Relative spectral responses and I-V characteristics were measured at 77 K. The R₀A product is used as an indicator of the dark current of photodiodes passivated with ZnS layer. A plot of R₀A values versus gate potential shows that the optimum R₀A values are obtained at small positive gate bias voltage. This dependence is consistent with surface recombination influencing the R₀A product. The results of a 2D model for calculating gate-induce surface leakage currents due to band-to-band tunneling are presented. The exact quantitative comparison cannot be made between our results and theory, since the active tunneling area is not known.

The RF magnetron sputtering growth and characteristics of ZnS and SiO₂ passivants on the surface of bulk n-type InAsSb have been reported. Our investigations include InAsSb surface preparation and in-situ pretreatment, deposition- induced surface damage, interface charge, and thermal stability. The metal-insulator-semiconductor test structures are processed and their electrical properties are measured by capacitance-voltage characteristics. The effect of sputtering growth conditions parameters (deposition temperature, pressure of argon, and RF power) is also reported. The sputtered ZnS layers exhibit excellent dielectric, insulating and mechano-chemical, as well as interface properties. The interfaces characterized by slight accumulation and small (after preservation of the thin natural oxide) hystereses are demonstrated. The SiO₂ layers have poor adherence and high density of pinholes. The samples with larger surface state densities have been observed.

Calculation has been carried out on the responsivity of an Al_xGa_1-xN(n)-GaN(p) photodiode ultraviolet detector in which the Al_xGa_1-xN layer has an energy band-gap grading. The analytical solution to the 1D continuity equation was used in the calculations. The spatial dependence of the material properties, such as the absorption coefficient and the energy band-gap of the photodiode n-type laser was included in the solution. The effect of the n-type front layer thickness of the energy band-gap graded photodiodes on the responsivity was analyzed and compared to that of the ungraded photodiodes. Compared to the ungraded photodiodes an enhanced current responsivity was found along with a greatly reduced dependence on the graded layer thickness and on surface recombination rate.

The conversion efficiency of solar energy into electrical energy by solar cells is limited by the conversion thermodynamics at about 30%. This efficiency can be improved if the incident solar radiation is absorbed not only in the basic but also in a graft-modified material of reduced volume (as a nanostructure). In this case the new material can form a substructure giving a complementary absorption which cannot be obtained in the classical way by an exclusively material modification. A new design of very- and ultra-high efficient solar cells has been conceived over the last years in which ion beam processing can be extensively employed. Our previous concepts, modeling and simulations have demonstrated that a considerable increase in silicon single-crystal Back Surface Field solar cell performance is possible. This mode of operation leads to a multilayer material superposition and a device design known as a multiinterface novel device. In this paper, a review of experimental results obtained on simplified multiinterface solar cells is presented. Measurements of optical absorption and carrier photogeneration carried out on structures modified by impurity implantation have confirmed the fundamental improvements by widened absorption and IR photogeneration which result in one of the possible Si material modifications. The observed results are encouraging. The increase in absorption (up to (lambda) <EQ 3200 nm) is the best yet measured. The IR photocurrent was first observed in a single-crystal Si device (the upper wavelength limit (lambda) <EQ 2500 nm was imposed by the measuring equipment). These results have been completed with other structural, optical and electronic measurements.