The effect of grading on the electrical behavior of Np AlGaAs/GaAs heterojunction diodes

We have studied the effect of compositional grading on the characteristics of N AlGaAs p GaAs heterojunction diodes, and have found that the elimination by grading of the heterojunction spike leads to a factor of 10 difference in the magnitude of current density. The behavior of heterojunction diodes has also been compared to GaAs homojunction diodes. Ideality factors for graded diodes were as good as n = 1.12, while those for the abrupt diodes were n = 1.25−1.30. At low forward-bias voltages the I–V characteristics are dominated by a recombination mechanism which leads to a temperature-independent logarithmic slope with applied bias. We also observe a difference in the built-in voltage between the graded-, abrupt- and homojunction diodes. By comparing the built-in voltage between abrupt heterojunction diodes and homojunction diodes, a value of ΔE_c = 0.64 ΔE_G for the conduction-band-edge discontinuity was obtained in excellent agreement with recent measurements on other device structures. An understanding of the current conduction mechanisms of these pN heterojunction diodes is essential for the understanding of GaAs/AlGaAs heterojunction bipolar transistors.     

Characterization of aluminum/LPCVD polysilicon Schottky barrier diodes

The I-V characteristics of aluminum Schottky diodes made on LPCVD deposited polysilicon with a wide range of doping concentration (8.5 × 10¹⁵−1.7 × 10²⁰ cm⁻³) have been investigated. Diodes with ideality factor n = 1.12 at room temperature were obtained with doping concentration ≤ 8.5 × 10¹⁶ cm⁻³. In contrast to large grain polysilicon, uniform I-V characteristics can be obtained across the wafer on fine grain LPCVD polysilicon. A barrier height of qφ_B0.73 eV at 300 K was consistently determined from both the I-V measurements and the specific contact resistance measurements. The contact resistance of aluminum/polysilicon contacts is well described by present theory except in the intermediate doping range.     

Capture cross sections of the gold donor and acceptor states in n-type Czochralski silicon

The hole and electron capture cross sections of the gold donor and acceptor have been measured directly in n-type silicon. The samples have been grown by the Czochralski technique and have originated from several different suppliers. They have been diffused with gold so that N_T ? 0.1 (N_D-N_A). Measurements have been made on both Schottky diodes and diffused junctions and similar results obtained from all samples. The electron cross section of the acceptor level was found to be (0.85±0.2) × 10^?16cm² and the hole cross section of the donor (3.5±0.8) × 10^?15cm², both were essentially temperature independent. The hole cross section of the acceptor was (0.9±0.2) × 10^?14cm² at 300 K and showed a T^?1.3 temperature dependence. The electron cross section of the donor was (0.9±0.2) × 10^?15cm² at 180 K with a T^?2 dependence.     

Contact potential of p-Al0.5Ga0.5As/n-GaAs structures

The built-in potential of Al_0.5Ga_0.5As (10¹⁸ cm^?3) gates on n-type (10¹⁷ cm^?3) GaAs channel layers in the case of heterojunction normally-off FETs has been measured via C-V and forward I-V methods. A built-in potential of 1.39 eV from C-V measurements and 1.36 eV from forward I-V characteristics which compare well with the theory (1.4 eV) have been deduced. The ideality coefficient is found to be 1.56.     

Effect of series resistance on the electrical characteristics and interface state energy distributions of Sn/p-Si (MS) Schottky diodes

In this study, electrical characteristics of the Sn/p-type Si (MS) Schottky diodes have been investigated by current-voltage (I-V) and capacitance-voltage (C-V) measurements at room temperature. The barrier height obtained from C-V measurement is higher than obtained from I-V measurement and this discrepancy can be explained by introducing a spatial distribution of barrier heights due to barrier height inhomogeneities, which are available at the nanostructure Sn/p-Si interface. A modified Norde’s function combined with conventional forward I-V method was used to extract the parameters including barrier height (Φ_b) and the series resistance (R_S). The barrier height and series resistance obtained from Norde’s function was compared with those from Cheung functions. In addition, the interface-state density (N_SS) as a function of energy distribution (E_SS-E_V) was extracted from the forward-bias I-V measurements by taking into account the bias dependence of the effective barrier height (Φ_b) and series resistance (R_S) for the Schottky diodes. While the interface-state density (N_SS) calculated without taking into account series resistance (R_S) has increased exponentially with bias from 4.235 × 10¹² cm⁻²eV⁻¹ in (E_SS - 0.62) eV to 2.371 × 10¹³ cm⁻²eV⁻¹ in (E_SS - 0.39) eV of p-Si, the N_SS obtained taking into account the series resistance has increased exponentially with bias from of 4.235 × 10¹² to 1.671 × 10¹³ cm⁻²eV⁻¹ in the same interval. This behaviour is attributed to the passivation of the p-doped Si surface with the presence of thin interfacial insulator layer between the metal and semiconductor.     

Metallic conductivity over an acceptor band of lightly compensated copper-doped p-Hg0.78Cd0.22Te crystals

The conductivity and Hall effect of heavily doped p-Hg_0.78Cd_0.22Te:Cu crystals were studied in the temperature range of 4.2–125 K. The conductivity over the impurity band is of a metallic type for the acceptor concentration N _A>3.8×10¹⁷ cm^?3. The conductivity and the Hall coefficient governed by the delocalized charge carriers in the impurity band are independent of temperature. The sign of the Hall effect is positive in the metallic conductivity range. Near the metal-insulator transition point, the Hall mobility increases linearly with the acceptor concentration and is independent of the acceptor concentration at N _A>1.6×10¹⁸ cm^?3. The metallic conductivity is proportional to N _A in the concentration range under study at N _A<3.1×10¹⁸ cm^?3. The Anderson transition occurs at the Cu concentration N _A=1.4×10¹⁷ cm^?3 in the A ⁺ impurity band, which is formed by positively charged acceptors. Minimum metallic conductivity corresponding to this transition equals 5.1 Ω^?1 cm^?1. It is shown that ?₂ conductivity in the subthreshold region is defined by delocalized carriers in the upper Hubbard band only for fairly heavy doping (N _A>1.4×10¹⁷ cm^?3). For N _A<1.4×10¹⁷ cm^?3, the hopping conductivity is observed.     

Gallium-oxide films obtained by thermal evaporation

The current-voltage (I–V), capacitance-voltage (C–V), and conductance-voltage (G–V) characteristics of metal/Ga _x O _y /GaAs/metal structures are investigated. Gallium-oxide films with a thickness of 150–170 nm are deposited by the thermal evaporation of Ga₂O₃ powder onto n-type GaAs substrates with the donor concentration N _d = 2 × 10¹⁶ cm^?3. Treatment of the Ga _x O _y films in oxygen plasma causes a decrease in both the forward and reverse currents and a shift of the C–V and G–V curves to higher positive voltages. The Fermi level at the insulator/semiconductor interface in the structures under study is unpinned. The density of states at the Ga _x O _y /GaAs interface is N _t = (2–6) × 10¹² eV^?1 cm^?2.     

Optical and transport properties of δ-doped pseudomorphic AlGaAs/InGaAs/GaAs structures

We investigate the effects of spacer layer thickness on the optical and transport properties of the n-typeδ-doped pseudomorphic Al_0.30Ga_0.70As/In_0.15Ga_0.85As / GaAs structures. Aδ-doped AlGaAs/InGaAs/GaAs structure with a 6nm spacer layer yields a sheet carrier concentration of 1.5×10¹² cm^?2 at 77K with electron mobility of 6.4×10³ cm²/Vs, 3.11×10⁴ cm²/Vs, and 3.45×10⁴ cm²/Vs at room temperature, 77 and 20K, respectively. The effects of the different scattering mechanisms on luminescence linewidth and electron mobility have also been discussed.     

The theoretical and experimental study on double-Gaussian distribution in inhomogeneous barrier-height Schottky contacts

We have considered multi-Gaussian distribution of barrier-heights for non-interactive barrier inhomogeneities in the inhomogeneous Schottky diodes, and we have shown the presence of the intersecting behavior in the forward-bias current-voltage (I-V) curves for the double-Gaussian distribution model at low temperatures. We have tried to eliminate this effect by generating I-V curves at lower temperatures with the bias-dependent barrier-height expression which leads to the ideality factors greater than unity. For this calculation, we have obtained the expressions for the barrier-height change and ideality factor, and for bias-dependency of the BH for the multi-Gaussian model by following the literature. We have shown that the experimental forward-bias I-V curves coincide with the theoretical ones using the bias-dependent inhomogeneous BH expression at low and high temperatures in the double-Gaussian distribution of BHs.     

Studies on vacuum deposited p-ZnTe/n-CdTe heterojunction diodes

The present paper reports the fabrication and detailed electrical characterization of p-ZnTe/n-CdTe heterojunction diodes prepared by vacuum deposition method. The possible conduction mechanisms of the heterojunction diode were determined by analyzing the I-V characteristics. The C-V characteristics of the heterojunction diodes were studied to determine the barrier height, carrier concentration and thickness of the depletion region in the heterojunction. A theoretical band diagram of the heterojunction was drawn based on Anderson’s model.     

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.     

Effect of Dislocation-related Deep Levels in Heteroepitaxial InGaAs/GaAs and GaAsSb/GaAs <Emphasis Type="Italic">p</Emphasis>–<Emphasis Type="Italic">i</Emphasis>–<Emphasis Type="Italic">n</Emphasis> Structures on the Relaxation time of Nonequilibrium Carriers

The results of an experimental study of the capacitance–voltage (C–V) characteristics and deep-level transient spectroscopy (DLTS) spectra of p⁺–p⁰–i–n⁰ homostructures based on undoped dislocationfree GaAs layers and InGaAs/GaAs and GaAsSb/GaAs heterostructures with homogeneous networks of misfit dislocations, all grown by liquid-phase epitaxy (LPE), are presented. Deep-level acceptor defects identified as HL2 and HL5 are found in the epitaxial p⁰ and n⁰ layers of the GaAs-based structure. The electron and hole dislocation-related deep levels, designated as, respectively, ED1 and HD3, are detected in InGaAs/GaAs and GaAsSb/GaAs heterostructures. The following hole trap parameters: thermal activation energies (E _t ), capture cross sections (σ _p ), and concentrations (N _t ) are calculated from the Arrhenius dependences to be E _t = 845 meV, σ _p = 1.33 × 10^–12 cm², N _t = 3.80 × 10¹⁴ cm^–3 for InGaAs/GaAs and E _t = 848 meV, σ _p = 2.73 × 10^–12 cm², N _t = 2.40 × 10¹⁴ cm^–3 for GaAsSb/GaAs heterostructures. The concentration relaxation times of nonequilibrium carriers are estimated for the case in which dislocation-related deep acceptor traps are involved in this process. These are 2 × 10^–10 s and 1.5 × 10^–10 s for, respectively, the InGaAs/GaAs and GaAsSb/GaAs heterostructures and 1.6 × 10^–6 s for the GaAs homostructures.     

Conductivity of Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>–GaAs Heterojunctions

The effect of annealing in argon at temperatures of T_an = 700–900°C on the I–V characteristics of metal–Ga₂O₃–GaAs structures is investigated. Samples are prepared by the thermal deposition of Ga₂O₃ powder onto GaAs wafers with a donor concentration of N _d = 2 × 10¹⁶ cm^–3. To measure theI–V characteristics, V/Ni metal electrodes are deposited: the upper electrode (gate) is formed on the Ga₂O₃ film through masks with an area of S _k = 1.04 × 10^–2 cm² and the lower electrode in the form of a continuous metallic film is deposited onto GaAs. After annealing in argon at T_an ≥ 700°C, the Ga₂O₃-n-GaAs structures acquire the properties of isotype n-heterojunctions. It is demonstrated that the conductivity of the structures at positive gate potentials is determined by the thermionic emission from GaAs to Ga₂O₃. Under negative biases, current growth with an increase in the voltage and temperature is caused by field-assisted thermal emission in gallium arsenide. In the range of high electric fields, electron phonon-assisted tunneling through the top of the potential barrier is dominant. High-temperature annealing does not change the electron density in the oxide film, but affects the energy density of surface states at the GaAs–Ga₂O₃ interface.     

A study of epitaxially stacked tunnel-junction semiconductor lasers grown by MOCVD

Design parameters of epitaxially stacked tunnel-junction asymmetric separate-confinement laser heterostructures are chosen. Technological modes for fabrication of heterostructures of this kind by metal-organic chemical vapor deposition in the system of AlGaAs/GaAs/InGaAs solid solutions are found. It is demonstrated that high-efficiency GaAs:Si/GaAs:C tunnel stru ctures and asymmetric AlGaAs/GaAs/InGaAs laser heterostructures with low internal optical loss can be fabricated in a single technological process. Conditions are chosen in which a deep mesa can be formed for fabrication of mesa-stripe diode lasers based on epitaxially stacked tunnel-junction laser heterostructures. Mesa-stripe diode lasers with a 150 × 12-μm aperture have been manufactured on the basis of these structures. These samples have a threshold current density J _th of 96 A cm^-2, internal optical loss α_i of 0.82 cm^-1, and differential resistance R = 280 mΩ. Samples containing three laser structures have a slope efficiency of 3 W A^-1 and a maximum peak output power of 250 W in the pulsed operation mode (100 ns, 1 kHz).     

Growth and characterization of GaSb bulk crystals with low acceptor concentration

GaSb bulk single crystals with low acceptor concentration were grown from a bismuth solution by the traveling heater method. The result is isoelectronic doping by Bi which gives a variation of the opto-electronic properties as a function of grown length as well as a pronounced microscopic segregation. Photoluminescence spectra at 4K show a decrease of the natural acceptor during growth, which is confirmed by Hall measurements. The electrical properties of this isoelectronic doped GaSb are hole concentrations and mobilities of N_A − N_D = 1.7 × 10¹⁶ cm⁻³ and μ = 870 cm²Vs at room temperature and N_A-N_D = 1 × 10¹⁶ cm⁻³ and μ = 4900 cm²/Vs at 77K, respectively. The lowest p-type carrier concentration measured at 300K is N_A − N_D = 3.3 × 10¹⁵ cm⁻³     

Thermally annealed Ni/n-GaAs(Si)/In Schottky barrier diodes

We have identically prepared as many as eight Ni/n-GaAs/In Schottky barrier diodes (SBDs) using an n-type GaAs substrate with a doping density of about 7.3 × 10¹⁵ cm⁻³. The thermal stability of the Ni/n-GaAs/In Schottky diodes has been investigated by means of current-voltage (I-V) techniques after annealed for 1 min in N₂ atmosphere from 200 to 700 °C. For Ni/n-GaAs/In SBDs, the Schottky barrier height Φ_b and ideality factor n values range from 0.853 ± 0.012 eV and 1.061 ± 0.007 (for as-deposited sample) to 0.785 ± 0.002 eV and 1.209 ± 0.005 (for 600 °C annealing). The ideality factor values remained about unchanged up to 400 °C annealing. The I-V characteristics of the devices deteriorated at 700 °C annealing.     

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.     

Autodoping effects of Ge in vapor-grown GaAsl-xPx layers on the Ge substrates

Epitaxial growth of GaAs_1-xP_x layer on the Ge substrate has been investigated under the optimized growth conditions for reducing vapor etching of the substrate, using a Ga-PCl₃-AsH₃-H₂ system. The free carrier concentration, ?N_D⁺?N_A^??, and the electroluminescent properties of GaAs_1-xP_x layers with $\text{x ? 0·4}$ are studied, and are correlated with the Ge concentration involved. In the lightly doped region below 1×10¹⁷ atoms/cm³, bright electroluminescence is observed at room temperature from forward-biased p-n junctions fabricated by a zinc-diffusion technique. However, in the narrow region of 1×10¹⁷?4×10¹⁷ atoms/cm³, the enhanced amphoteric behavior of Ge leads to concentration quenching of visible-light emission. The ?N_D⁺?N_A^?? reaches its maximum at ～ 1×10¹⁷ atoms/cm³. Nearly complete self-compensation is observed above 4×10¹⁷ atoms/cm³ due to the increase of the concentration of deep-lying Ge acceptors.     

Analysis of interface states and series resistance of MIS Schottky diodes using the current-voltage (I-V) characteristics

The purpose of this paper is to analyze interface states in Al/SiO₂/p-Si (MIS) Schottky diodes and determine the effect of SiO₂ surface preparation on the interface state energy distribution. The current-voltage (I-V) characteristics of MIS Schottky diodes were measured at room temperature. From the I-V characteristics of the MIS Schottky diode, ideality factor (n) and barrier height (Φ_B) values of 1.537 and 0.763 eV, respectively, were obtained from a forward bias I-V plot. In addition, the density of interface states (N_ss) as a function of (E_ss-E_v) was extracted from the forward bias I-V measurements by taking into account both the bias dependence of the effective barrier height (Φ_e), n and R_s for the MIS Schottky diode. The diode shows non-ideal I-V behaviour with ideality factor greater than unity. In addition, the values of series resistance (R_s) were determined using Cheung’s method. The I-V characteristics confirmed that the distribution of N_ss, R_s and interfacial insulator layer are important parameters that influence the electrical characteristics of MIS Schottky diodes.