Exciton characteristics of intercalated TlGaSe2 single crystal

It is shown that lithium-ion intercalation of TlGaSe₂ single crystal leads to a shift of the exciton peak associated with the direct edge toward longer wavelengths (ΔE=15 meV at 5 K). As a result, the temperature shift of the exciton peak in TlGaSe₂(∂E ^ex/∂T) decreases more than twofold in absolute value to −1.1×10⁻⁴ eV/K at 20≲T≲105 K and −0.25×10⁻⁴ eV/K at 5≲T≲20 K. Lithium-ion (Li⁺) intercalation of TlGaSe₂ has almost no effect on the energy position of the exciton associated with indirect transitions. Fiz. Tekh. Poluprovodn. 32, 145–147 (February 1998)     

The effect of annealing temperature on the carrier concentration OF Hg0.6Cd0.4Te

The carrier concentration dependence of Hg_0.6Cd_0.4Te on annealing temperature for the Hg and Te saturation condi-tions is presented in this paper. At low annealing tempera-tures, T_A < 350‡ C, residual donor impurities apparently limit the carrier concentration. In contrast, at higher annealing temperatures, 350‡ C < T < 700‡ C, the stoichio-metric acceptor density is increased such that the residual donors are compensated and the material is converted to p-type with an acceptor density as large as 10¹⁷ cm⁻³ . An empirical expression describing this dependence of the acceptors on annealing temperature is given for both the Hg and Te saturation condition: P (Hg saturation) = 1.46 × 10²² exp (−0.84/kT_A), P (Te saturation) = 1.90 × 10¹⁸ exp (−0.15/kT_A). Supported in part by Air Force Materials Laboratory, WPAFB, Ohio under Contract AF61533-C-74-5041.     

Structures and physical properties of sputtered amorphous SiC films

Optical and electrical properties have been measured for amorphous SiC films prepared by rf sputtering in a pure Ar atmosphere with a sintered 6H-SiC target. The absorption edge E₀ determined from the relation of αhΝ = B(hΝ-E₀)² ranged from 1.45 to 1.80 eV depending on the film thickness and the substrate temperature. The room temperature electrical conductivity is in the range of 5.4×10⁻¹¹ and 1.4×10⁻⁵ Ω⁻¹cm⁻¹. The absorption edge decreases and the conductivity increases with increasing film thickness. The absorption edge shifts to shorter wavelengths (blue shift) and the conductivity decreases during annealing below 400‡C for 60 min, whereas the absorption edge shifts to the longer wavelength side (red shift) and the conductivity increases during annealing at 800‡C It is proposed that the two annealing processes cause structural changes in amorphous SiC films, one of which involves removal of defects or voids while the other involves rearrangement or rebonding of the component atoms.     

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)     

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)     

Deep electron levels in undoped polycrystalline CdTe annealed in liquid Cd

The method of deep-level transient spectroscopy (DLTS) is used to determine the set of deep electron levels in undoped n-CdTe polycrystals grown by chemical synthesis from vapor phase in highly nonequilibrium conditions and then subjected to annealing in liquid Cd. After annealing, the electron concentration is found to increase from ∼10⁸ to 10¹⁵ cm⁻³. Electron traps with deep levels E ₁ = 0.84 ± 0.03 eV and E ₂ = 0.71 ± 0.02 eV with total concentration ∼10¹⁴ cm⁻³ are dominant in the DLTS spectrum. The role of grain boundaries and intrinsic point defects in formation of deep-level centers and their effect on the value of conductivity after annealing are discussed. A relation between the level E ₁ and complexes of intrinsic point defects and relation of the level E ₂ to the Cd _i point defect are considered.     

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.     

Lpe growth of Hgl−xCdxTe using conventional slider boat and effects of annealing on properties of the epilayers

The epitaxial layers of Hg_1−xCd_xTe (0.17≦×≦0.3) were grown by liquid phase epitaxy on CdTe (111)A substrates using a conventional slider boat in the open tube H₂ flow system. The as-grown layers have hole concentrations in the 10¹⁷− 10¹⁸ cm⁻³ range and Hall mobilities in the 100−500 cm²/Vs range for the x=0.2 layers. The surfaces of the layers are mirror-like and EMPA data of the layers show sharp compositional transition at the interface between the epitaxial layer and the substrate. The effects of annealing in Hg over-pressure on the properties of the as-grown layers were also investigated in the temperature range of 250−400 °C. By annealing at the temperature of 400 °C, a compositional change near the interface is observed. Contrary to this, without apparent compositional change, well-behaved n-type layers are obtained by annealing in the 250−300 °C temperature range. Sequential growth of double heterostructure, Hg_l−xCd_xTe/Hg_l−yCd_yTe on a CdTe (111)A substrate was also demonstrated.     

Fabrication of blocked impurity-band structures on gallium-doped silicon by plasma hydrogenation

The electrical characteristics of blocked impurity-band structures (BIB-structures) based on gallium-doped silicon (N _Ga≈5×10¹⁷ cm⁻³) are investigated. The blocking layers were formed by passivation of the gallium impurity by means of treatments in an rf-discharge hydrogen plasma at substrate temperatures T=20–220 °C. It is found that the activation energy E _a of the hopping conductivity with hopping between nearest gallium neighbors decreases from 8.7 meV (before hydrogenation) to 1.3 meV (after hydrogenation at T=220 °C). The current-voltage characteristics and temperature dependence of the dark current of the structures and their change after isochronal (t=20 min) annealing at temperatures T=220–400 °C are determined. The current-voltage characteristics of the structures at low temperatures are calculated. The results of calculations are found to agree with experimental data. Fiz. Tekh. Poluprovodn. 31, 311–317 (March 1997)     

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)     

High temperature annealing of mnos devices and its effect on si-nitride stress,interface charge density and memory properties

The effects of high temperature annealing in N₂ and H₂ ambients upon the following properties of MNOS devices have been investigated: Si-nitride stress, etch rate, index of refraction, fixed interface charge and fast surface state density, memory window and charge retention at elevated temperatures. The CVD Si-nitride and Si-oxynitride films were deposited at temperatures as low as 610°C with a NH₃/SiH₄ ratio of 1000:1, the heat treatments were performed in the temperature range from 640°C to 1130°C. A similar N₂-annealing behavior was found for film stress and flatband voltage. The film stress increased with increasing annealing time and temperature while the interface charge density changed from high positive values (Q_N/q = 4 × 10¹²cm⁻2) after nitride deposition at 610°C to high negative values (Q_N/q = -4 × 10¹²cm⁻2) after annealing at 930°C, The fast interface state density increased while the charge retention time was drastically reduced. The changes of the properties by N₂ annealing are mainly attributed to decomposition of SiH and NH bonds. Minor effects were obtained by annealing in H₂ and the drastic changes caused by N₂ annealing could be reversed to a great extent by subsequent H₂ annealing. Finally the different effects of deposition and annealing temperature on the propertiesare discussed .     

Temperature-Dependent Studies of Si-Implanted Al<Subscript>0.33</Subscript>Ga<Subscript>0.67</Subscript>N with Different Annealing Temperatures and Times

Electrical activation studies were carried out on Si-implanted Al_0.33Ga_0.67N as a function of ion dose, annealing temperature, and annealing time. The samples were implanted at room temperature with Si ions at 200 keV in doses ranging from 1 × 10¹⁴ cm⁻² to 1 × 10¹⁵ cm⁻², and subsequently proximity-cap annealed from 1150°C to 1350°C for 20 min to 60 min in a nitrogen environment. One hundred percent electrical activation efficiency was obtained for Al_0.33Ga_0.67N samples implanted with a dose of 1 × 10¹⁵ cm⁻² after annealing at either 1200°C for 40 min or at 1300°C for 20 min. The samples implanted with doses of 1 × 10¹⁴ cm⁻² and 5 × 10¹⁴ cm⁻² exhibited significant activations of 74% and 90% after annealing for 20 min at 1300°C and 1350°C, respectively. The mobility increased as the annealing temperature increased from 1150°C to 1350°C, showing peak mobilities of 80 cm²/V s, 64 cm²/V s, and 61 cm²/V s for doses of 1 × 10¹⁴ cm⁻², 5 × 10¹⁴ cm⁻², and 1 × 10¹⁵ cm⁻², respectively. Temperature-dependent Hall-effect measurements showed that most of the implanted layers were degenerately doped. Cathodoluminescence measurements for all samples exhibited a sharp neutral donor-bound exciton peak at 4.08 eV, indicating excellent recovery of damage caused by ion implantation.     

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)     

Electrical Activation Studies of Silicon-Implanted Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>N with Aluminum Mole Fraction of 11% to 51%

Electrical activation studies of Si-implanted Al _x Ga_1−x N with an Al mole fraction of 11% to 51% have been carried out as a function of ion dose and annealing temperature. The Al _x Ga_1−x N samples were implanted at room temperature with Si ions at 200 keV in doses ranging from 1 × 10¹⁴ cm⁻² to 1 × 10¹⁵ cm⁻², and subsequently annealed from 1100°C to 1350°C for 20 min in a nitrogen environment. The maximum electrical activation efficiencies for the Al _x Ga_1−x N samples with an Al mole fraction less than 40% were obtained for samples implanted with the highest Si dose of 1 × 10¹⁵ cm⁻². On the other hand, for the Al _x Ga_1−x N samples with an Al mole fraction more than 40%, nearly perfect activation efficiencies of 99% and 100% were obtained for the samples implanted with the lowest Si dose of 1 × 10¹⁴ cm⁻². The mobility of the Si-implanted Al _x Ga_1−x N samples increased with increasing annealing temperature in spite of the increased number of ionized donors and thus increased impurity scattering, indicating that a greater amount of lattice damage is being repaired with each successive increase in annealing temperature. These results provide suitable annealing conditions for Si-implanted Al _x Ga_1−x N-based devices with an Al mole fraction from 11% to 51%.     

Density measurement of Sn-40Pb,Sn-57Bi,and Sn-9Zn by indirect Archimedean method

By the indirect Archimedean method, the density and the density-temperature relationship of the Sn-40Pb eutectic alloy and two Pb-free solders, Sn-57Bi and Sn-9Zn eutectic alloys, were measured from room temperature to about 250°C. The results showed that the density-temperature dependence for each alloy in both solid and melting states can be fitted linearly as ρ_S(Sn-40Pb)=8.51−8.94×10⁻⁴(T−25°C), ρ_L(Sn-40Pb)=8.15−13.8×10⁻⁴(T−T_m); ρ_S(Sn-57Bi)=8.54−5.86 × 10⁻⁴(T−25°C), ρ_L(Sn-57Bi)=8.51−10.9×10⁻⁴(T−T_m); and ρ_s(Sn-9Zn)=7.22−7.78×10⁻⁴(T−25°C), ρ_L(Sn-9Zn)=6.89−5.88×10 ⁻⁴(T−T_m), where the density unit was g/cm³. At the melting point, density of the melt of these solders is 8.15 g/cm³, 8.51 g/cm³, and 6.89 g/cm³, respectively. The density decreased 2.6% for Sn-40Pb eutectic alloy during melting, and 2.7% for Sn-9Zn eutectic alloy, but increased 0.5% for Sn-57Bi eutectic alloy. The excess molar volume for these alloys after mixing at their melting point is 0.03 cm³/mol for Sn-40Pb, 0.09 cm³/mol for Sn-57Bi, and 0.21 cm³/mol for Sn-9Zn.     

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)     

Si-defect concentrations in heavily Si-DOPED GaAs: annealing-Induced changes-II

Isothermal annealing produces changes in the free carrier density, defect-induced localized vibrational mode (LVM) infrared absorption, microstructure as measured by transmission electron microscopy (TEM), and critical resolve shear stress of heavily Si-doped GaAs. The changes have been measured and correlated for three different Si concentrations for several annealing temperatures. The measurements reveal temperature dependent annealing-induced changes in several specific defect concentrations. The observations indicate the following behavior for two ingots with [Si] ≳ 2 × 10¹⁹ cm⁻¹³: (1) when the anneal temperature, T_A = 400°C, the concentration of Si_ga donors, as determined from LVM spectra decreases probably due to the generation of V_Ga defects followed by the formation of Si_Ga-V_Ga pairs. This change is responsible for observed decreases in carrier density and the large increase in yield stress. The yield stress shows a dependence of the form σ-σ_o ∝ [Si_Ga-V_Ga]^1/4. (2) When T_A = 500°C, the LVM spectra indicate that all of the observed Si defect concentrations change. The decrease in [Si_Ga] alone cannot explain the decrease in carrier density, and a previous suggestion that a new acceptor is required is confirmed. Both the LVM measurements and the shear stress indicate that only a small fraction of the [Si_Ga] reduction is by the formation of Si_Ga-V_Ga pairs. (3) When T_A = 700°C, a new acceptor is still required and the other experimental observations at T_A = 500°C are also still seen here. There is a large decrease in [Si_Ga] and [Si_As] observed for short anneal times which coincides with the formation of Si-rich extrinsic loops and the loop area/vol increases with [Si]. (4) When T_A > 700°C, all of the changes become smaller as T_A increases. For lower [Si] ~ 1.5 × 10¹⁸ cm⁻³, no significant annealing-induced changes are observed for any of the T_A given above.     

Nearly Perfect Electrical Activation Efficiencies from Silicon-Implanted Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>N with High Aluminum Mole Fraction

Electrical activation studies of Al _x Ga_1−x N (x = 0.45 and 0.51) implanted with Si for n-type conductivity have been made as a function of ion dose and anneal temperature. Silicon ions were implanted at 200 keV with doses ranging from 1 × 10¹⁴ cm⁻² to 1 × 10¹⁵ cm⁻² at room temperature. The samples were subsequently annealed from 1150°C to 1350°C for 20 min in a nitrogen environment. Nearly 100% electrical activation efficiency was successfully obtained for the Si-implanted Al_0.45Ga_0.55N samples after annealing at 1350°C for doses of 1 × 10¹⁴ cm⁻² and 5 × 10¹⁴ cm⁻² and at 1200°C for a dose of 1 × 10¹⁵ cm⁻², and for the Al_0.51Ga_0.49N implanted with silicon doses of 1 × 10¹⁴ cm⁻² and 5 × 10¹⁴ cm⁻² after annealing at 1300°C. The highest room-temperature mobility obtained was 61 cm²/V s and 55 cm²/V s for the low-dose implanted Al_0.45Ga_0.55N and Al_0.51Ga_0.49N, respectively, after annealing at 1350°C for 20 min. These results show unprecedented activation efficiencies for Al _x Ga_1−x N with high Al mole fractions and provide suitable annealing conditions for Al _x Ga_1−x N-based device applications.     

Deep-level transient spectroscopy of radiation-induced levels in 6H-SiC

The methods of capacitance and current deep level transient spectroscopy are used to investigate single crystals of Leli n-SiC(6H) irradiated by 5-MeV electrons at doses of 10¹⁶–10¹⁸ cm⁻². Eleven deep levels belonging to the resulting radiation-induced intrinsic defects were observed in the energy range 0.18–1.44 eV from the bottom of the conduction band. Isochronous annealing of various samples showed that most of the observed defects were stable up to a temperature of ∼1000 °C. In addition, annealing of a deep level with ionization energy E _i=0.48–0.53 eV was observed in the temperature range 150–250 °C. It is believed that this center is caused by a vacancy in the carbon sublattice. Fiz. Tekh. Poluprovodn. 33, 1314–1319 (November 1999)     

Circular and linear enhancement-mode 6H-SiC MOSFETs for high temperature applications

Direct current measurements are performed up to 673K at circular and linear (shown in parenthesis) enhancement-mode metal oxide semiconductor field effect transistors (MOSFETs). These devices are fabricated on a p-type 6H-SiC epitaxial layer with a doping concentration N_A ≈ 1 × 10¹⁶ cm⁻¹. The n⁺ source/drain regions and the p⁺ regions for the channel stops are achieved by ion implantation of nitrogen and aluminum, respectively. Both MOSFET geometries show excellent output characteristics with a good saturation behavior even at elevated temperatures. The inversion layer mobility μ_n extracted in the linear region is 38 cm²·V⁻¹·s⁻¹ (35 cm²·V⁻¹·s⁻¹) and reveals a weak dependence on temperature with a maximum of 46 cm²·V⁻¹·s⁻¹ (42 cm²·V⁻¹·s⁻¹) at about 473K. Regarding the transfer characteristics, the drain current I_D can be well modulated by the gate-source voltage V_GS resulting in an I_on/L_off-ratio of 10⁸ (10⁸) at 303K and 10⁵ (10⁶) at 673K. In the subthreshold regime, I_D can be pinched off well below 10 pA with a subthreshold swing of 150 mV/decade (155 mV/decade) at room temperature. The threshold voltage V_T as a function of temperature shows two linear sections with negative temperature coefficients of −6.8 mV·K⁻¹ (−6.8 mV·K⁻¹) from 303 to 423K and −2.5 mV·K⁻¹ (−2.0 mV·K⁻¹) from 423 to 673K. By measuring V_T as a function of bulk-source voltage V_BS at different temperatures, N_A can be directly estimated at a transistor and gives 9.6 × 10¹⁵ cm⁻³ (9.8 × 10¹⁵ cm⁻³). The measured bulk Fermi potential Φ_f of the p-type epitaxial layer deviates less than 10% from the calculated value at a given temperature.