Rectification in AlxGa1-xAs-GaAs N-n heterojunction devices

The previously unsolved problem of rectification at Al_xGa_1-xAs-GaAs N-n heterojunction is found to originate from a vague concept regarding the maximum junction grading width which can sustain rectification. The theoretical current density vs voltage characteristics of this heterojunction system are derived from thermionic emission theory. It is found that, unless the impurity concentration of the AlGaAs layer (prepared by LPE techniques) is less than 10¹⁶ cm^?3, typical 90–200 Å metallurgical grading widths at the N-n heterojunction interface produce either ohmic or poorly rectifying characteristics. These results explain (1) the lack of rectification in most N-n Al_xGa_1-xAs-GaAs heterojunctions reported in the literature and (2) the recent observation of significant rectification in high purity (N)Al_0.3Ga_0.7As-(n)GaAs heterojunctions reported by Chandra and Eastman.     

Analysis of characteristics of photodetectors based on InGaAs heteroepitaxial structures for 3D imaging

The 320 × 256 focal plane arrays based on р ⁺ -B–n-N ⁺ tetralayer heterostructures with a wide-gap barrier layer have been investigated. The heterostructures with a narrow-gap n-InGaAs absorbing layer were grown by means of metalorganic vapor phase epitaxy on InP substrates. The band discontinuity between the In_0.53Ga_0.47As absorbing layer and the In_0.52Al_0.48As barrier layer is removed by growing a thin four-component n-AlInGaAs layer with the bandgap gradient variation. Delta-doped layers included into the heterostructures make it possible to lower the barrier in the valence band and eliminate the nonmonotonicity of energy levels. The experimental study of the dark current has been performed. It has been revealed that the average value of the dark current does not exceed 10 fA for the photodiode arrays with a pitch of 30 μm.     

Aluminum-silicon Schottky barriers as semiconductor targets for EBS devices

The ideal semiconductor target for EBS devices is most closely approximated by the Schottky barrier junction, with Al having the highest figure of merit. Accordingly, large area (1·27 mm²), high-field AlnSi Schottky barrier junctions surrounded by a p-n junction guard-ring have been fabricated in unpassivated, SiO₂ passivated, and Al₂O₃ passivated configurations. The fabrication procedure is described and data pertaining to forward and reverse characteristics, yield and storage characteristics are presented.The Schottky barrier height is characterized by four independent measurements with excellent agreement between the various measurements. The barrier height is in the 0·710–0·760 V range and the typical ideality factor is ≤1·05. The devices exhibit ideal Schottky barrier behavior at least over the ?50?100°C temperature range.The current gain of Schottky barriers with different Al layer thicknesses is measured under static electron bombardment over the 1–30 keV energy range. From these measurements, the average energy required to create a hole-electron pair is determined to be 3·44±0·2 eV. Using the gain-energy characteristic, it is possible to identify an optimum accelerating potential for each target. This optimum accelerating potential is in good agreement with that obtained theoretically from consideration of target losses. No junction instability is observed due to electron irradiation for beam current densities up to 0·314 A/cm² and target current densities exceeding 1000 A/cm². Further, no significant device degradation is observed for target dissipated power densities exceeding 50 kW/cm².Under pulse mode dynamic testing, output pulses of 13·1 A with a measured risetime of 0·72 nsec into the 10 Ω optimum load are obtained. When the output risetime is corrected for beam resetime (～0·60 nsec), an output/risetime of 13·1 A/0·40 nsec is obtained. This is within a factor of 2 of the theoretical output capability of an optimized target; the difference is due to the capacitance of the guard-ring. The amplifier pulse mode efficiency is 85 per cent. The low pass bandwidth is 875 MHz, and the Pf² figure is 82 W-GHz². In addition, small-signal transconductance and power gains of 4·35 ? and 40 dB, respectively, are achieved.No output pulse distortion or pulse height deterioration is noted for pulse widths up to 130 nsec having 13·0 A amplitude under prolonged bombardment of our devices. This indicates that if any insulator charging is occurring, it does not result in any deleterious effects on the target performance.     

Electrical and optical properties of AgInS2

Crystal sizes of AgInS₂ grown by a directional freezing depend on sulphur pressures at the preparation. The conductivity is only n-type and nominally undoped AgInS₂ has the resistivity of 25 Ω-cm and the Hall mobility of 64 cm²/V sec. Sulphur vacancies of AgInS₂ become electron-trapping levels in the forbidden band. It is obtained from the measurements of thermally stimulated current that the levels lie at E_T1 = 0·19±0·01 eV and E_T2 = 0·40±0·01 eV, and the concentrations depend on sulphur pressures at the crystal preparations. AuAgInS₂ contacts operate as a Schottky barrier diode and the barrier height is 0·97 eV. AgInS₂ has a dichroism because of its uniaxial lattice structure. The transition is direct for $\text{E}\text{⊥c}$ and indirect for $\text{E}\text{∥c}$, and the values for the energy gap are E_g^⊥ = 1·88±0·01 eV and E_g^∥ = 1·77±0·01 eV, respectively.     

Temperature dependence of residual stress in epitaxial GaAs/Si(100) films determined from photoreflectance spectroscopy data

In the temperature range T=10–300 K, photoreflectance spectroscopy was used to study the temperature dependence of residual stress in epitaxial n-GaAs films (1–5 μm thick, electron concentration of 10¹⁶–10¹⁷ cm⁻³) grown on Si(100) substrates. A qualitative analysis showed that the photoreflectance spectra measured in the energy region of the E ₀ transition in GaAs had two components. They consisted of the electromodulation component caused by the valence subband |3/2; ±1/2〉-conduction band transition and the low-energy excitonic component. The magnitude of stress was determined from the value of the strain-induced energy shift of the fundamental transition from the subband |3/2; ±1/2〉 with respect to the band gap of the unstressed material E ₀(T)-E ₀ ^{|3/2; ±1/2〉} (T). The increase in the energy shift E ₀-E ₀ ^{|3/2; ±1/2〉} from 22 ± 3 meV at 296 K to 29 ± 3 meV at 10 K, which was found in the experiments, gives evidence of an increase in biaxial stress with decreasing temperature. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 34, No. 1, 2000, pp. 73–80. Original Russian Text Copyright ? 2000 by Kuz’menko, Ganzha, Bochurova, Domashevskaya, Schreiber, Hildebrandt, Mo, Peiner, Schlachetzki.     

Radiation effects and interphase interactions in ohmic and barrier contacts to indium phosphide as induced by rapid thermal annealing and irradiation with γ-ray 60Co photons

The radiation resistance of Au-Pd-Ti-Pd-n ⁺⁺-InP ohmic contacts and Au-TiB _x -n-n ⁺-n ⁺⁺-InP barrier contacts—both initial and subjected to a rapid thermal annealing and irradiated with ⁶⁰Co γ-ray photons with doses as high as 10⁹ R—has been studied. Before and after external effects, the electrical characteristics of the barrier and ohmic contacts, distribution profiles for components, and phase composition in the metallization layers have been measured. In ohmic Pd-Ti-Pd-Au contacts subjected to rapid thermal annealing and irradiation, a significant distortion of the layered structure of metallization occurs; this distortion is caused by the thermal and irradiation-stimulated transport of Pd over the grain boundaries in polycrystalline Ti and Au films. However, the specific contact resistance ρ _c does not change appreciably, which is related to a comparatively unvaried composition of the contact-forming layer at the Pd-n ⁺-InP interface. In the initial sample and the sample subjected to the rapid thermal annealing at T = 400°C with the Au-TiB _x -n-n ⁺-n ⁺⁺-InP barrier contacts and irradiated with the dose as high as 2 × 10⁸ R, a layered structure of metallization is retained. After irradiation with the dose as high as 10⁹ R, in the samples subjected to a rapid thermal annealing at T = 400°C, the layered structure of metallization becomes completely distorted; however, this structure is retained in the initial sample. The electrical properties of the contact structure appreciably degrade only after irradiation of the sample preliminarily subjected to a rapid thermal annealing at T = 400°C.     

Forward I-V characteristics of Pt/n-GaAs Schottky barrier contacts

The forward I-V characteristics of Pt/n-GaAs planar Schottky diodes and the effect of high temperature annealing on these characteristics have been investigated. Near-ideal (thermionic emission theory) I-V characteristics with an ideality factor n ≈ 1·00–1·09 and a barrier height φ_B ≈ 0·90–0·95 V are obtained for diodes made on as-received GaAs. On annealing at 350°C in vacuum, n remains practically unchanged although φ_B increases by ≈ 5–6 per cent and rather large currents are detected at voltages <0·3 V, which are attributed to the recombination centers created during alloying.For diodes made on GaAs which was preannealed in air at 350°C, non-ideal behavior is observed with φ_B ≈ 0·79–0·80 V and n ≈ 1·29. After annealing at 350°C in vacuum, n gradually decreases to 1·07 whereas φ_B increases to 0·96 V. Recombination currents are now observed at lower voltages. After further annealing at 350°C in air, n increases, φ_B decreases and recombination currents at lower voltages are no longer observed. A mechanism is proposed to explain the observed forward I-V characteristic behavior.     

<Emphasis Type="Italic">p</Emphasis><Superscript>+</Superscript>-Si-<Emphasis Type="Italic">n</Emphasis>-CdF<Subscript>2</Subscript> heterojunctions

Boron diffusion and the vapor-phase deposition of silicon layers are used to prepare ultrashallow p⁺-n junctions and p⁺-Si-n-CdF₂ heterostructures on an n-CdF₂ crystal surface. Forward portions of the I–V characteristics of the p⁺-n junctions and p⁺-Si-n-CdF₂ heterojunctions reveal the CdF₂ band gap (7.8 eV), as well as allow the identification of the valence-band structure of cadmium fluoride crystals. Under conditions in which forward bias is applied to the p⁺-Si-n-CdF₂ heterojunctions, electroluminescence spectra are measured for the first time in the visible spectral region.     

Pentacene/n-Si heterojunction diodes and photovoltaic devices investigated by I-V and C-V measurements

The forward and reverse current density-voltage (J-V) and capacitance-voltage (C-V) characteristics of pentacene/n⁻-silicon heterojunction diodes were investigated to clarify the carrier conduction mechanism at the organic/inorganic heterojunction. Current rectification characteristics of the pentacene/n⁻-Si junctions can be explained by a Schottky diode model with an interfacial layer. The diode parameters such as Schottky barrier height and ideality factor were estimated to be 0.79-1.0 eV and 2.4-2.7, respectively. The C-V analysis suggests that the depletion layer appears selectively in the n⁻-Si layer with a thickness of 1.47 μm from the junction with zero bias and the diffusion potential was estimated at 0.30 eV at the open-circuit condition. The present heterojunction allows the photovoltaic operation with power conversion efficiencies up to 0.044% with a simulated solar light exposure of 100 mW/cm².     

Electronic properties of Pb1−xHgxSSi heterojunctions

Two types of heterojunctions have been prepared by electroless deposition of Pb_1?xHg_xS (x = 0–0.33) films with α′ and β′ structures on n-type silicon single crystal substrates. Functional behaviour of the forward characteristics is explained on the basis of band to band tunnelling coupled with the recombination processes. The energy band diagram is given for both types of Pb_1?xHg_xS/Si heterojunctions in agreement with the experimental results.     

Carrier Transport Mechanism and Band Offsets at the Interface of ZnS/<Emphasis Type="Italic">n</Emphasis>-Si (111) Heterojunctions Fabricated by Vacuum Thermal Evaporation

The electrical properties and band offset of ZnS/n-Si(111) heterojunctions with and without annealing were analyzed. The result showed that the rectifying characteristics of ZnS/n-Si(111) heterojunctions became better and the leakage current increased after annealing. This phenomenon is mostly due to the volatilization of S atoms of ZnS films and leads to defect levels appearing at the interface of the ZnS/n-Si(111) hetrojunctions. The valence band offset (ΔE _V) of the ZnS/n-Si(111) heterojunctions can be calculated to be ?0.7 ± 0.15 eV by means of photoelectron spectroscopy, indicating that the band offsets of ZnS/n-Si(111) heterojunctions show a type-II band alignment.     

The role of the interface insulator layer and interface states on the current-transport mechanism of Schottky diodes in wide temperature range

In order to interpret in detail the experimentally observed current-voltage-temperature (I-V-T) and capacitance-voltage-temperature (C-V-T) results of Al/p-Si metal-semiconductor Schottky barrier diodes (SBDs) we have been examined the samples in the temperature range of 150-375 K. In the calculation method, to confirm the relationship between the I-V-T and C-V-T results, we have reported a modification which includes the ideality factor, n, and tunnelling parameter δχ^1/2 in the forward bias current characteristics. In the intermediate bias voltage region (0.1 < V < 0.6 V), the semi-logarithmic plots of the forward I-V-T curves were found to be linear. From the reverse saturation currents I₀ obtained by extrapolating the linear region of curves to zero applied voltage, the values of zero bias barrier heights ?_B0 were calculated at each temperature. The values of ideality factor calculated from the slope of each curves were plotted as a function of temperature. The values of n are 3.41-1.40 indicating that the Al/p-Si diode does obey the thermionic field emission (TFE) mechanism rather than the other transport mechanism, particularly at low temperature. The high value of ideality factors is attributed to high density of interface states in the SBDs. The temperature dependence energy density distribution profile of interface state was obtained from the forward bias I-V-T measurements by taking into account the bias dependence of the effective barrier height and ideality factor. The interface states density N_ss decreasing with increasing temperature was interpreted by the result of atomic restructuring and reordering at the metal-semiconductor interface. After the modification was made to the forward current expression, we obtained a good agreement between the values of barrier height obtained from both methods over a wide temperature.     

dependence of the energy spectrum of a strained ZnSe/ZnS superlattice on the charge-carrier concentration

The model of self-consistent electron-deformation coupling was used to show that additional periodic local electron-deformation wells and barriers arise in the vicinity of heterocontact in a strained ZnSe/ZnS superlattice within the main quantum well (ZnSe) and above the main barrier (ZnS). It is found that, for the thickness of the ZnSe overgrown layer in the range from 10 to 20 Å, the electron ground-state energy E _0c decreases steadily with increasing conduction-electron concentration n _c ; however, for the layer thickness exceeding 20 Å, the concentration dependence E _0c =f(n _c ) becomes nonmonotonic and features a maximum, which shifts to lower concentrations n _c as the layer thickness increases.     

Electrical characterization of MS and MIS structures on AlGaN/AlN/GaN heterostructures

The forward and reverse bias I-V, C-V, and G/ω-V characteristics of (Ni/Au) Schottky barrier diodes (SBDs) on the Al_0.22Ga_0.78N/AlN/GaN high-electron-mobility-transistor (HEMTs) without and with SiN_x insulator layer were measured at room temperature in order to investigate the effects of the insulator layer (SiN_x) on the main electrical parameters such as the ideality factor (n), zero-bias barrier height (Ф_B0), series resistance (R_s), interface-state density (N_ss). The energy density distribution profiles of the N_ss were obtained from the forward bias I-V characteristics by taking into account the voltage dependence of the effective barrier height (Ф_e) and ideality factor (n_V) of devices. In addition, the N_ss as a function of E_c-E_ss was determined from the low-high frequency capacitance methods. It was found that the values of N_ss and R_s in SBD HEMTs decreases with increasing insulator layer thickness.     

Minority carrier injection in GeAg Schottky diodes

The J-V characteristics at T = 300°K for Schottky barrier AgGe(N) are presented, the resistivity of the germanium substrate being $\text{ρ = 0·23 Ω}\text{cm}$ and $\text{ρ = 10 Ω}\text{cm}$. The values of _n(J～exp (qV/nkT)) greater than unity found in the J-V characteristics are attributed to minority carrier injection phenomenon. The observation of the series resistance modulation for the higher injection levels confirms this hypothesis.     

Use of a Schottky barrier to measure impact ionization coefficients in semiconductors

The use of a Schottky barrier to determine the impact ionization coefficients of electrons and holes in semiconductors has been studied analytically and also evaluated experimentally by comparing the results for silicon with those already available in the literature.The Schottky barrier offers several advantages over a diffused p-n junction in such measurements. Pure electron initiation and pure hole initiation can be separately achieved. The abrupt barrier provides an accurately known electric field, and the linearity of the field distribution simplifies the problem of extracting the ionization coefficients from the multiplication data.We present a general solution of the charge multiplication equation and derive expressions for the ionization coefficients for the particularly simple conditions that can be achieved in a Schottky-barrier junction. Our results for silicon in the range 2 × 10⁵ < E < 4 × 10⁵V/cm can be expressed in the form $\text{α = α}{}_{\mathrm{\infty }}\text{exp}\text{(}\text{?b}{}_{\mathrm{n}}\text{E}\text{)}$ for electrons and $\text{β = β}{}_{\mathrm{\infty }}\text{exp}\text{(}\text{?b}{}_{\mathrm{p}}\text{E}\text{)}$ for holes, with α_∞ = 9·2 × 10⁵ cm^?1, β_∞ = 2·4 × 10⁵ cm^?1, b_n = 1·45 × 10⁶ V/cm and b_b = 1·64 × 10⁶ V/cm.     

‘Modulation effect by intense hole injection’ in epitaxial silicon Schottky-barrier-diodes

The forward characteristics of different epitazial n-n⁺ silicon Schottky barrier diodes have been studied up to high current densities. Modulation has been observed in these experiments, that means an increase in charge carrier density in the series resistance region, i.e. in the epitaxial n-layer. By appropriate analysis of the forward characteristics the carrier density can be determined as a function of the current density. In accordance with the predictions of Scharfetter we find that the modulation increases with the barrier height but decreases with rising donor density. Furthermore it is shown how modulation is affected by recombination centres. The modulation effect is attenuated by irradiation with 1·5 MeV electrons and in a similar manner by doping the epitaxial layer with gold.     

Growth of CdGeAs2 single crystals by the chemical vapor transport method

We have grown CdGeAs₂ single crystals by chemical vapor transport (CVT), a method not previously applied for this compound. The crystallographic data of this chalcopyrite (cell parametersa ₀ = 5.9456 ± 0.0001Å, c₀ = 11.2131 ± 0.0007Å) and its electrical transport properties are reported. Predominantly n-type crystals are obtained (at RTn = 1 · 10¹⁷cm?3, μⁿ = 2000 cm²(Vs)^?1). Vacuum heat treatment at 500° C yields a type conversion fromn- to p-type. In all p-type samples the minority carrier mobility is calculated to be larger than 10000 cm²(Vs)^?1.     

Effective electron mass in heavily doped GaAs in the ordering of impurity complexes

Spectra of edge photoluminescence (PL) at 300 K have been studied in a set of Czochralski-grown Te-doped GaAs single crystals with a free carrier density of n₀=10¹⁷–10¹⁹ cm^?3. The carrier density dependences of the chemical potential and band gap narrowing are obtained by analyzing the PL spectral line profiles. The dependence of the effective mass of electrons at the bottom of the conduction band on their density, m ₀ ^* (n₀), is calculated. It is shown that the nonmonotonic m ₀ ^* (n₀) dependence correlates with data on electron scattering in the material under study and results from the ordering of impurity complexes.