Optical absorption in PbGa2Se4 single crystals

Optical measurements are performed in a PbGa2Se4 single crystal. The nature of the optical transitions is determined in the interval of photon energies 2.24–2.46 eV in the temperature range 77–300 K. It is shown that indirect and direct optical transitions take place in the energy intervals 2.28–2.35 eV and 2.35–2.46 eV, corresponding to E _gi =2.228 eV and E _gd =2.35 eV, respectively, at 300 K. The temperature coefficients of E _gi and E _gd are equal to −0.6×10⁻⁴ eV/K and −4.75×10⁻⁴ eV/K, respectively. Fiz. Tekh. Poluprovodn. 33, 39–41 (January 1999)     

Optical properties of gallium nitride bulk crystals grown by chloride vapor phase epitaxy

The optical properties of bulk crystals of gallium nitride grown by chloride vapor-phase epitaxy are investigated. It is shown that these crystals exhibit exciton luminescence bands. Analysis of the energy positions of the band maxima imply certain conclusions about the presence or absence of mechanical stresses in the bulk crystals of GaN obtained. Analysis of the luminescence spectra also reveals that the temperature dependence of the width of the GaN band gap E _g in the temperature range T=6–600 K is well described by the expression E _g (T)=3.51−7.4×10⁻⁴ T ²(T+600)⁻¹ eV. It is estimated that values of the free electron concentration in these crystals do not exceed 10¹⁸ cm⁻³. The optical characteristics of the bulk GaN crystals are compared analytically with literature data on bulk crystals and epitaxial layers of GaN grown by various methods. Fiz. Tekh. Poluprovodn. 33, 1173–1178 (October 1999)     

High purity InP grown by chemical beam epitaxy

A Hall mobility as high as 176,200 cm²V⁻¹ s⁻¹ at 77 K withN _d -N _a =1.3×10¹⁴ cm⁻³ has been obtained by adjusting the substrate and the phosphine cracker temperatures. The 2 K photoluminescence spectra show finely resolved excitonic transitions for layers grown above 535° C with linewidths of 0.07 meV. Excitonic transitions have been recorded between 2 and 250 K. The free exciton energy position leads to a highly accurate expression of the band gap energy, which extrapolates toE _g =1.347 eV at 300 K.     

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)     

Frenkel’-Poole effect for boron impurity in silicon in strong warming electric fields

A method based on measurement of the thermally stimulated conductivity of a weakly compensated semiconductor, which is doped with a deep impurity and which contains an impurity component that is shallower than the main component, has been developed for investigating the Frenkel’-Poole effect. The results of an investigation of the thermally stimulated conductivity of Si:Ga samples with gallium density N _A =(2–3)×10¹⁸ cm⁻³ and low accompanying impurity content (⩽10¹³ cm⁻³) are reported. The conductivity was measured after extrinsic photoexcitation of samples heated at a rate β=0.6 K/s in the temperature range T=4.2–24 K in electric fields E=20–1000 V/cm. It is shown that the maximum on the curves of the thermally stimulated conductivity is due to the thermally stimulated emptying of the boron impurity and shifts to lower values of T as E increases. The decrease of the ionization energy of impurity B in an electric field, which turns out to be somewhat weaker than the field according to the Frenkel’-Poole model for singly charged Coulomb centers, is found from the shift of the maximum. Fiz. Tekh. Poluprovodn. 31, 777–780 (July 1997)     

Electrical properties of epitaxial indium arsenide and narrow band solid solutions based on it

The electrical properties of epitaxial InAs and solid solutions based on it (InGaAsSb, InAsSbP, InAsGa, InAsP) have been investigated. It is shown that intentionally undoped crystals have n-type conductivity, which is determined by shallow donor impurities (E ₁=0.002–0.003 eV) and structural defects (E ₂=0.02–0.03 eV and E ₃=0.09–0.10 eV). It is shown that growth of epitaxial InAs using the neutral solvent Pb and also rare-earth elements makes it possible to reduce the electron density by almost an order of magnitude (to levels as low as 3×10¹⁵ cm⁻³) due to due to a decrease in the density of structural defects. Fiz. Tekh. Poluprovodn. 33, 781–788 (July 1999)     

Effect of electron irradiation on the electrical properties of n-type Pb1−x SnxTe (x⋍2) alloys

The effect of electron bombardment (T _in⋍300 K, E=6 MeV, Φ⩽4×10¹⁷ cm⁻²) on the electrical properties of n-type Pb_1−x Sn_xTe has been studied. Electron bombardment decreases the electron concentration and produces conductivity-type n-p conversion. The difference rate of the donor-and acceptor-type defect generation as a result of bombardment has been determined. Anomalies are detected in the temperature and magnetic-field dependences of the electrical parameters of the bombardment samples. These anomalies are associated with the appearance of a hole-enriched surface layer as a result of electron bombardment. Fiz. Tekh. Poluprovodn. 31, 264–267 (March 1997)     

Nuclear magnetic resonance spectra of 119Sn and 125Te in SnTe and SnTe:Mn

A study is reported of the nuclear magnetic resonance spectra of ¹¹⁹Sn and ¹²⁵Te in SnTe with hole concentrations p ₇₇=1.42×10²⁰−2.3×10²¹ cm⁻³ and in SnTe:Mn (N _Mn=0.5 and 5 at. %, p ₇₇=8×10²⁰ cm⁻³) at T=4.2–300 K. Considerable broadening of NMR lines due to hyperfine magnetic interactions between nuclear and electron spins was observed in SnTe with p ₇₇>2ײ⁰ cm⁻³. Asymmetric broadening of the resonance lines was observed in the rhombohedral phase of SnTe and SnTe:Mn. The temperature dependence of the NMR line width of ¹²⁵Te in SnTe:Mn is in agreement with the magnetic phase diagram for N _Mn=5 at. %. The superparamagnetic phase of SnTe:Mn is formed at T=20±2 K and the ferromagnetic phase is formed at T=4.2 K. Fiz. Tekh. Poluprovodn. 31, 1187–1191 (October 1997)     

Deep Traps in AlGaN/GaN Heterostructure Field-Effect Transistors Studied by Current-Mode Deep-Level Transient Spectroscopy: Influence of Device Location

Across-wafer variation of deep traps in AlGaN/GaN heterostructure field- effect transistors (HFETs) has been studied using current-mode deep-level transient spectroscopy (I-DLTS). It is found that applying a bias to the gate corresponding to open-channel or nearly pinched-off operation while cooling from 550 K has significant effects on the threshold voltage of the device and spectral features of I-DLTS at T <~400 K. To compare I-DLTS spectra acquired under different measurement conditions (e.g., different filling pulse heights or widths), attention should be paid to the gate bias applied while cooling. We find that the spectral features observed across the wafer can be divided into three categories: (i) a dominant trap A ₁ at ~360 K; (ii) a prominent hole-like trap H ₁ at ~480 K; and (iii) for T < 340 K, several traps varying in magnitude, including A, B, and C ₁, and a hole-like trap H ₀. Based on I-DLTS, measured as a function of filling pulse height and filling pulse width, we suggest that: (i) trap A ₁, with E _T = 1.1 eV to 1.2 eV and σ = 4 × 10⁻¹³ cm² to 2 × 10⁻¹² cm², is associated with extended defects, such as threading dislocations; (ii) traps A, B, and C ₁, located mainly in the two-dimensional electron gas (2DEG) channel region, could be related to point defects; and (iii) the hole-like trap H ₁, with E _T = 1.2 eV to 1.3 eV and σ = 8 × 10⁻¹⁷ cm² to 5 × 10⁻¹⁵ cm², may be related to surface states. Note that traps A (~0.67 eV), B (0.58 eV to 0.61 eV), and C ₁ (0.44 eV to 0.49 eV) are commonly observed in GaN layers grown by various techniques. For all of the HFETs near the center of the wafer, trap A ₁ dominates the DLTS spectra, whereas trap B becomes prominent for some of the HFETs near the edge of the wafer.     

Electronic properties and deep traps in electron-irradiated <Emphasis Type="Italic">n</Emphasis>-GaN

The study is concerned with the effect of electron irradiation (with the energies E = 7 and 10 MeV and doses D = 10¹⁶−10¹⁸ cm⁻²) and subsequent heat treatments in the temperature range 100–1000°C on the electrical properties and the spectrum of deep traps of undoped (concentration of electrons n = 1 × 10¹⁴−1 × 10¹⁶ cm⁻³), moderately Si-doped (n = (1.2−2) × 10¹⁷ cm⁻³), and heavily Si-doped (n = (2−3.5) × 10¹⁸ cm⁻³) epitaxial n-GaN layers grown on Al₂O₃ substrates by metal-organic chemical vapor deposition. It is found that, on electron irradiation, the resistivity of n-GaN increases, this is due to a shift of the Fermi level to the limiting position close to E _c −0.91 eV. The spectrum of deep traps is studied for the initial and electron-irradiated n-GaN. It is shown that the initial properties of the irradiated material are restored in the temperature range 100–1000°C, with the main stage of the annealing of radiation defects at about 400°C.     

DEEP LEVEL DEFECTS IN SI-IMPLANTED LEC UNDOPED Si-GaAs

The residual electrically active defects in(4×10~(12)cm~(-2)(30KeV)+5×10~(12)cm~(-2)(130KeV))si-implanted LEC undoped si-GaAs activated by two-step rapid thermal annealing(RTA)LABELED AS 970℃(9S)+750℃(12S)have been investigated with deep level transient spec-troscopy(DLTS).Two electron traps ET_1(E_c-0.53eV,σ_n=2.3×10~(-16)cm~2)and ET_2(E_c-0.81eV,σ_n=9.7×10(-13)cm~2)are detected.Furthermore,the noticeable variations of trap's con-centration and energy level in the forbidden gap with the depth profile of defects induced by ion im-plantation and RTA process have also been observed.The[As_i·V_(As)·As_(Ga)]and[V_(As)·As_i·V_(Ga)·As_(Ga)]are proposed to be the possible atomic configurations of ET_1 and ET_2,respectively to explaintheir RTA behaviors.     

Influence of fast-neutron irradiation on the intensity of the copper-related luminescence band at hν m =1.01 eV in n-type GaAs

The influence of neutron irradiation (the energy E=2 MeV and the dose Φ=10¹³–10¹⁵cm⁻²) and subsequent anneals (the annealing temperature T _a =400–700 °C and the annealing time is 30 min) of n-type GaAs(Te,Cu) crystals with an initial carrier concentration n ₀=2×10¹⁸ cm⁻³ on the intensity of the copper-related luminescence band with an emission maximum at hν _m =1.01 eV is studied. A significant irradiation-induced increase in the intensity of the band is observed. It is attributed to a radiation-stimulated increase in the concentration of emitting centers (Cu_Ga V _As pairs) as a result of the effective interaction of interstitial copper atoms with irradiation-induced gallium (V _Ga) and arsenic (V _As) vacancies, as well as V _Ga V _As divacancies. Fiz. Tekh. Poluprovodn. 31, 1171–1173 (October 1997)     

Kinetics of the accumulation of radiation defects during the high-dose electron irradiation of Pb1−x SnxSe alloys

The kinetics of the variation of the electron concentration in electron-irradiated (T≈300 K, E=6 MeV, Φ⩽7.1×10¹⁷ cm⁻²) n-Pb_1−x Sn_xSe (x=0.2 and 0.25) alloys in the vicinity of the metal-insulator transition induced by electron irradiation are investigated. The principal parameters of the energy spectrum of the irradiated alloys are determined by comparing the experimental and theoretical dependences of the electron concentration on fluence. It is shown that agreement between the theoretical and experimental data is possible only under the assumption that the defect production rate decreases with increasing fluence, and a model, within which the main defect formation mechanism in the alloys investigated is the formation of complexes of primary radiation defects with structural defects typical of the as-grown crystals, is proposed. Fiz. Tekh. Poluprovodn. 32, 1409–1413 (December 1998)     

Energy spectrum of n-type Pb1−x SnxTe (x=0.22) bombarded by neutrons

The effect of hydrostatic pressure (P⩽12 kbar) on the electrical properties of n-type Pb_1−x Sn_xTe (x=0.22) bombarded by electrons (T≈300 K, E=6 MeV, Φ=7.7×10¹⁷ cm⁻²) has been investigated. The restructuring of the energy spectrum of electronirradiated alloys under pressure has been investigated. The parameters of a model of the energy spectrum of charge carriers in electron-irradiated n-type Pb_1−x Sn_xTe (x=0.22) have been determined on the basis of the experimental data obtained. Fiz. Tekh. Poluprovodn. 31, 1021–1023 (August 1997)     

Heterojunction diodes in 3C-SiC/Si system grown by reactive magnetron sputtering: Effects of growth temperature on diode rectification and breakdown

3C-SiC/Si heterojunction diodes were prepared by reactive magnetron sputtering of pure Si in CH₄-Ar discharge on Si(111) substrates kept at temperatures (T_s) ranging from 800 to 1000°C. A good diode rectification process started for films grown at T_s≤900°C. Heterojunction diodes grown at T_s = 850°C showed the best performance with a saturation current density of 2.4 × 10⁻⁴ A cm⁻². Diode reverse breakdown was obtained at a voltage of −110 V. The doping concentration (N_d) of the 3C-SiC films was calculated from 1/C² vs V plot to be 3 × 10¹⁵ cm⁻³. Band offset values obtained were −0.27 and 1.35 eV for the conduction and valence band, respectively. X-ray diffraction analysis revealed the film grown at T_s = 850°C to be single-phase 3C-SiC. The full width at half maximum of the 3C-SiC(111) peak was only 0.25 degree. Cross-sectional transmission electron microscopy showed the film to be highly (111)-oriented with an epitaxial columnar structure of double positioning domain boundaries.     

A Study of Deep Defect Levels in Semi-Insulating SiC Using Optical Admittance Spectroscopy

Optical admittance spectroscopy (OAS), supported by electron paramagnetic resonance (EPR) measurements, is used to identify the controversial vanadium acceptor levels in vanadium-doped semi-insulating (SI) 4H-SiC and 6H-SiC. The V^3+/4+ levels for the cubic site are likely located at E _c − 0.67 ± 0.02 eV and E _c − 0.70 ± 0.02 eV in 6H-SiC and E _c − 0.75 ± 0.02 eV in 4H-SiC. A peak at 0.87 ± 0.02 eV in the 6H-SiC is tentatively assigned to the same transition at the hexagonal site and the associated transition in 4H-SiC is thought to occur near 0.94 eV. All assignments are supported by the observation of V³⁺ in the EPR spectrum.     

Effect of successive implantation of Ag+(Cu+) and Xe+ ions on the recombination properties of CdxHg1−x Te crystals

The effect of successive double implantation of Ag⁺(Cu⁺) and Xe⁺ ions on the recombination properties of Cd_xHg_1−x Te (0.2<x<0.3) crystals has been investigated. It is shown that after implantation of ions of one chemical element, followed by diffusion thermal annealing at temperatures below 150–200 K, recombination through local levels lying 30±5 meV below the conduction band bottom dominates. Successive double implantation of Ag⁺(Cu⁺) and Xe⁺ ions followed by diffusion thermal annealing changes the course of the temperature dependence of the lifetime of the nonequilibrium charge carriers. It was determined that for Cd_xHg_1−x Te crystals with x⋍0.20–0.25 in the temperature interval 700–200 K the lifetime of the nonequilibrium charge carriers is low (τ<0.15 μs) and does not depend on the temperature. For Cd_xHg_1−x Te crystals with x⋍0.3 recombination of nonequilibrium charge carriers occurs through two types of levels: in the temperature range 140–200 K — deep levels E _t1⋍E _c −51 meV and at lower temperatures (77–140 K) — through shallower levels E _t2⋍E _c −(16±2) meV. Fiz. Tekh. Poluprovodn. 31, 786–789 (July 1997)     

Doping and impurity compensation by ion implantation in a-SiGe films

This paper discusses the electrical properties of a-SiGe films (N _Ge∼2.2 at. %) prepared by co-evaporation of Si and Ge from separate sources and doped by ion implantation of substitutional impurities (B⁺ and P⁺), as well as the results of controlled impurity compensation by ion-beam doping. It was found that B⁺ and P⁺ implantation into a-SiGe films in the dose range 1.3×10¹⁴–1.3×10¹⁷ cm⁻², followed by annealing at 350 °C, increased the conductivity of these films from 10⁻⁹ to 10⁻⁴ and to 10⁻⁵ S/cm for B⁺ and P⁺, respectively. The position of the Fermi level could be varied from (E _v+0.27) to (E _c−0.19) eV. These investigations indicate that compensation of pre-doped a-SiGe films by ion implantation is feasible and reproducible. It is also found that higher doping efficiency of a-SiGe films is obtained by using boron than by using phosphorus. Fiz. Tekh. Poluprovodn. 32, 1260–1262 (October 1998)     

Amorphous hydrogenated silicon films exhibiting enhanced photosensitivity

Amorphous hydrogenated silicon (a-Si:H) films with photoconductivities as high as 10⁶, i.e., exceeding the photoconductivity of “standard” a-Si:H by two orders of magnitude, are investigated. The dark conductivity (σ _d ) of the films has an activation energy ΔE=0.85–1.1 eV. The photoconductivity σ _ph is measured at a photocarrier generation rate of 10¹⁹ cm⁻³ · s⁻¹ and photon energy ɛ=2 eV. Several distinctive characteristics are ascertained in the behavior of σ ^ph and σ _d as functions of ΔE and also in the spectral curve and decay kinetics of σ _ph during prolonged illumination. It is concluded that the investigated material holds major promise for photovoltaic device applications. Fiz. Tekh. Poluprovodn. 33, 110–113 (January 1999)     

Spreading resistance and compensation of charge carriers in ferromagnetic silicon implanted with manganese

Profiles of impurity distribution and spreading resistance have been studied in the layers of ferromagnetic silicon obtained by implantation of Mn (or Co). Standard wafers of n- and p-Si with a high or low electrical conductivity were implanted with Mn ions with the dose (1−5) × 10¹⁶ cm⁻². It is found that, as a result of postimplantation annealing in vacuum for 5 min at 850°C, Mn manifests itself as an amphoteric impurity and compensates acceptors in high-resistivity p-Si and donors in low-resistivity n-Si. It is shown that only an insignificant fraction of Mn ions (1–2%) is electrically active and is involved in compensation. The magnitude of compensation is used to determine energies of the levels E _c − 0.12 eV for n-Si and E _v + 0.32 eV for p-Si; these levels are attributed to Mn ions at interstitial sites in the silicon crystal lattice, i.e., (Mn _i )^−/0 and (Mn _i )^+/++, respectively.