Effect of deep impurity on electric characteristics of epitaxial GaAs structures

The electric characteristics of the p ⁺-i-n ⁺ structures are analyzed for two types of GaAs epitaxial layers: the structures with an i layer based on undoped GaAs and an i layer based on GaAs:Cr. The forward currents of the first-type diodes are caused by recombination in the space-charge region. The reverse I–V characteristics at the voltages to 10–15 V are determined by the component of the generation current. At |U| > 20 V, the current growth is caused by the Poole-Frenkel effect, which is replaced by electron tunneling through the potential-barrier top with increasing the voltage as a result of the electron-phonon interaction. The forward branches of the I–V characteristics of the p ⁺-i-n ⁺ diodes with the i layer based on GaAs:Cr are explained by the unipolar injection in the semiconductor, which is replaced by the bipolar injection with increasing the voltage. The reverse I–V characteristics are linear in the range of 1–15 V; at |U| > 20 V, an increase in current is caused by the impact ionization.     

Effect of charged dislocation walls on mobility in GaN epitaxial layers

A theoretical model in the context of a conventional representation on traditional notion concerning Read cylinders for interpretation of mobility collapse as a function of the concentration of free carriers in GaN-based films is suggested. Along with phonon and impurity scattering mechanisms, electron scattering due to charged dislocations embedded into the walls is taken into account in the model. An expression is obtained for the height of the drift barrier depending on the concentration of free carriers. Based on the derived equations, the dependence of the location of the mobility minimum on the dislocation structure is interpreted.     

Inversion of the impurity conductivity sign in As2Se3:Bi films deposited by two different methods

It is demonstrated that As₂Se₃:Bi _x films deposited by thermal evaporation have p-type impurity conductivity, whereas films of the same composition, produced by ion-plasma cosputtering in vacuum exhibit n-type impurity conductivity. On the basis of these results, a new method is suggested for the fabrication of p-n homojunctions in film structures made of chalcogenide glassy semiconductors doped with bismuth in various ways.     

Control of impurity density in homoepitaxial semiconductor layers grown by sublimation at UHV

Sublimation at UHV has good prospects as a technique for growing thin epitaxial layers in which out-diffusion of impurities from the substrate must be avoided. It has been shown[1] that after a source has been used for some time the layer resistivity approaches the starting value for the source material. This paper presents a simple theoretical model which explains this empirical observation and can be used to determine more general conditions for the control of impurity density in homoepitaxial semiconductor films grown by sublimation at UHV.     

Features of the electrical compensation of bismuth impurities in PbSe

Self-compensation is studied in bulk samples of PbSe: (Bi, Se_ex) prepared by a metal-ceramic method. The dependence of the carrier concentration on the amount of excess selenium is investigated for various bismuth concentrations. Comparison of the experimental data with calculated data shows that the donorlike activity of bismuth accommodated in the cation sublattice is compensated by doubly ionized lead vacancies. Nonmonotonic behavior of the dependence of the carrier concentration on the selenium excess is observed in some series of samples due to the incorporation of Bi atoms into both the cation and anion sublattices. Fiz. Tekh. Poluprovodn. 32, 775–777 (July 1998)     

LPE growth of crack-free PbSe layers on Si(100) using MBE-Grown PbSe/BaF2CaF2 buffer layers

Crack-free PbSe on (100)-oriented Si has been obtained by a combination of liquid phase epitaxy (LPE) and molecular beam epitaxy (MBE) techniques. MBE is employed first to grow a PbSe/BaF₂/CaF₂ buffer structure on the (100)-oriented Si. A 2.5 μm thick PbSe layer is then grown by LPE. The LPE-grown PbSe displays excellent surface morphology and is continuous over the entire 8×8 mm² area of growth. This result is surprising because of the large mismatch in thermal expansion coefficients between PbSe and Si. Previous attempts to grow crack-free PbSe by MBE alone using similar buffer structures on (100)-oriented Si have been unsuccessful. It is speculated that the large concentration of Se vacancies in the LPE-grown PbSe layer may allow dislocation climb along higher order slip planes, providing strain relaxation.     

Formation and reconstruction of Se nanoislands at the surface of thin epitaxial ZnSe layers grown on GaAs substrates

Strained epitaxial ZnSe layers are grown on GaAs substrates by the method of vapor-phase epitaxy from metal-organic compounds. It is found that Se nanoislands with a density of 10⁸ to 10⁹ cm^–2 are formed at the surface of such layers. It is established that an increase in the size of Se islands and a decrease in their density take place after completion of growth. Annealing in a H₂ atmosphere at a temperature higher than 260°C leads to the disappearance of Se islands and to a decrease in the surface roughness. It is shown that annealing does not lead to deterioration of the structural perfection of the epitaxial ZnSe films; rather, annealing gives rise to a decrease in the intensity of impurity–defect luminescence and to an increase in the intensity of intrinsic radiation near the bottom of the exciton band.     

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.     

Features of impurity photoconductivity in Si:Er/Si epitaxial diodes

The photocurrent spectra of Si:Er/Si epitaxial diode structures are studied. It is shown that the nature of the sub-band-gap photoresponse is determined by the epitaxial growth temperature of the Si:Er layer and is not related to the composition of erbium emission centers. It is found that the absorption of light with photon energies lower than the energy-gap of silicon is determined by impurity-defect complexes that appear during the growth of the epitaxial layer and form a quasi-continuous spectrum of states in the energy gap of silicon. It is assumed that these impurity centers are not related to optically active erbium centers and are not involved in excitation-energy transfer to the rare-earth impurity.     

Measurement of minority carrier lifetime and diffusion length in silicon epitaxial layers by means of the photocurrent technique

A new method for the determination of minority carrier lifetime and diffusion length in thin silicon epitaxial layers was developed. Using a transparent MIS structure the surface recombination velocity was reduced below 25 cm/s. This method makes possible to determine minority carrier lifetime and also diffusion length much greater than the thickness of the epitaxial layer.     

Improved thermal stability of Ni-silicides on Si:C epitaxial layers

The thermal stability of Ni-silicides on tensily strained in situ P doped Si:C epitaxial layers was evaluated. The baseline Ni silicidation process was shown to be compatible with Si:C Recessed Source-Drain (RSD) stressors for NMOS strain engineering while the thermal stability of NiSi:C contacts was significantly improved compared to NiSi ones. Dominant degradation mechanism was shown to be the transition to the NiSi₂:C phase. It was demonstrated that the Si:C strain level affects the silicide formation but has no significant effect on the NiSi:C thermal stability. A mechanism responsible for the improved thermal stability of NiSi:C silicides is discussed.     

Effect of compositional dependence on physicochemical properties of Bi2Se3 doped system

Crystalline bulk compositions of Bi₂ (Se_1−xTe_x)₃ system with ( x=0.0–1.00) were prepared using the conventional melting method. The structural properties of bulk samples were studied with the aid of XRD and SEM analysis. Compositional element distribution and elemental ratios were estimated with EDX spectroscopy that attached with SEM. XRD patterns show that the prepared compounds are crystalline materials with single phases of Bi₂Se₃ and Bi₂Te₃ and/or a ternary phase. The grain size calculations were performed using the well-known Scherrer equation. The thermal studies analysis was carried out by using DSC. DSC studies revealed that the prepared samples are stable and none decomposable over the temperature range. Physicochemical properties such as compactness, molar volume and the free volume percentage were calculated for the concerned alloys based on the experimentally calculated densities of each compound. The measured parameters showed a strong dependence on the Te content.     

Effect of carrier gas on the surface morphology of V-doped GaN layers

Vanadium-doped GaN (GaN:V) have been elaborated by metalorganic chemical vapour deposition (MOCVD). We have used vanadium tetrachloride (VCl₄) to intentionally incorporate vanadium (V) during the crystal growth of GaN. The films were grown on sapphire substrate with tow procedures. A series of layers were elaborated under nitrogen (N₂) and another under hydrogen (H₂). For the growth of GaN:V in hydrogen atmospheric, we have used the SiN treatment consisting of an exposure of sapphire substrate to a mixture of ammonia (NH₃) and silane (SiH₄). In-situ laser reflectometry analysis show that the surface morphology of layers depends on VCl₄ flow rate and the growth conditions. The experiments show that the quality of the grown layers (as measured with X-ray diffractometer (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) increases under N₂.     

Conductivity of Se95As5 chalcogenide glassy semiconductor layers containing the EuF3 rare-earth impurity in high electric fields

By investigating the I?CV characteristics of an Al-Se₉₅As₅:EuF₃-Te structure, it is established that, upon the application of a positive potential to Te, the current flows in it by the mechanism of space-charge-limited currents (SCLCs) of unipolar-injection, and the N-type I-V characteristic is observed for the opposite polarity. It is shown that these are processes of the thermal-field ionization of neutral and negatively charged U ^? centers, which play a dominant role in the current-flow mechanism in the investigated structures upon the application of an electric field with intensities exceeding 10⁵ V/cm. These are also processes of the electron-hole recombination and capture of charge carriers at U ^? centers. The energy position and concentration of the local states, which correspond to the indicated centers and characterize the effect of the electric field??activation length are determined. It is established that it is the EuF₃ impurities that predominantly affect the local-state concentration.     

Doping of epitaxial layers and heterostructures based on HgCdTe

Available publications concerned with doping of epitaxial layers of HgCdTe alloys and heterostructures based on these alloys are reviewed. The main changes in technology of HgCdTe doping, which occurred when device structures fabricated on the basis of bulk material were replaced by those based on epitaxial layers are analyzed. The specific features of the doping of HgCdTe epitaxial layers in the course of the growth of these layers by the liquid-phase epitaxy, metal-organic chemical vapor deposition, and molecular-beam epitaxy are considered. The electrical properties of the doped material are analyzed. The current concepts of the intrinsic defects in HgCdTe and the effect of these defects on the properties of HgCdTe are briefly considered.     

Characteristics of diffused P-N junctions in epitaxial layers

A one-dimensional analysis has been made to determine properties of diffused p-n junctions in epitaxial layers with nonuniform impurity concentration. Impurity diffusion from the surface and from the substrate is assumed to have complementary error function distribution. The transcendental equations obtained by analytical integration of Poisson's equation were evaluated numerically with the IBM 7090/94. Junction depth, impurity gradient and impurity level at the junction are given for a variety of diffusion parameters and impurity concentrations. In addition, graphs are presented, showing the relationship between reverse voltage and depletion layer thickness, capacitance per unit area, and peak electric field for the case of silicon. A comparison between the actual impurity profile and the usual linear approximation using the impurity gradient at the junction gives the range of depletion layer thickness or reverse voltage in which such an approximation is justified. Further, examples are presented of the electric field distribution in the depletion layer for several impurity concentration profiles. Calculated and experimentally determined values of some readily accessible junction characteristics show reasonably good agreement.     

Liquid phase epitaxial growth of InAsxSbyPl-x-y layers on InAs

High quality InAs_xSb_yP_l-x-y quaternary layers, which are lattice matched to InAs, have been grown successfully on InAs substrates by liquid phase epitaxy. Both Graded and constant composition InAs_xSb_yP_l-x-y layers have been grown. In addition, the graded InAs_xSb_yP_l-x-y layer has been used as a buffer layer for the growth of InAs_l-xSb_x on an InAs substrate. Research supported in part by Commander, U. S. Army Missile Command, Attn: AMSMI-RNS, Redstone Arsenal, AL 35809 and ARPA-Advanced Research Projects Agency, 1400 Wilson Boulevard, Arlington, VA 22209.     

Analytic evaluation of diffused impurity layers in silicon

An analytic method is outlined for the calculation of average conductivity of diffused layers in silicon for a complementary error function and Gaussian impurity profiles and the results are found to be in good agreement with those obtained by the numerical integration method. It is shown that the results for Gaussian distribution are obtained directly from the derivations for an error-function distribution. The method is also useful for the estimation of the temperature coefficient of the diffused layers.