Process and device characterization of high voltage gallium arsenide P-i-N layers grown by an improved liquid phase epitaxy method

GaAs P-i-N layers with an i-region net doping of less than 10¹² cm⁻³ were grown on P⁺ and N⁺ substrates by a modified liquid phase epitaxy (LPE) method. Doping profiles and structural data obtained by varius characterization techniques are presented and discussed. A P⁺-P-i-N-N⁺ diode with a 25 μm-wide i-region exhibits a breakdown voltage of 1000 V, a t_rr of 50 ns, and reverse current densities (at V_R = 800 V) of − 3 × 10⁻⁶ A/cm² at 25°C and 10⁻² A/cm² at 260° C.     

Leakage currents of np silicon diodes with different amounts of dislocations

Leakage currents in n⁺p silicon planar-diodes appeared to be related to the presence of dislocations, revealed by an X-ray topographic technique, in and near the n⁺ regions. Electrical measurements revealed a dominant bulk recombination—generation level, 0·055 eV. below the middle of the energy gap, and with τ_p0/τ_n0 >1. This latter fact indicates a donor type defect. Surface recombination-generation currents were minimized by using a MOS type guard ring.     

Modeling multi-band effects of hot electron transport in silicon by self-consistent solution of the Boltzmann transport and Poisson equations

This paper presents a self-consistent numerical technique for the solution of the multi-band Boltzmann transport equation (BTE) and the Poisson equation in silicon. The effects of high energy bands ( 3 eV) are modeled in the formulation. The numerical technique utilizes a new curvilinear boundary-fitted coordinate grid which is tailored for self-consistent calculations. A new Scharfetter-Gummel like discretization of the BTE is presented. The numerical algorithm is tested on a n⁺ − n − n⁺ device structure.     

Single-unit system with corrective maintenance at random checks governed by probabilities in a geometric progression

A system which comprises only one unit and a single server is considered. While the unit is in operation, at random intervals it is subjected to checks for corrective maintenance (CM). While the unit is under CM, it is also working and thus may fail. The probabilities that the unit will not undergo CM at random checks are in geometric progression (p, p², p³,…), whereas the probabilities that the unit will undergo CM are (1 − p, 1 − p²,…). We consider three models, and obtain the mean time to system failure and steady-state availability of the system for these models.     

Experimental studies of switching in metal semi-insulating n-p silicon devices

The switching properties of silicon structures comprising a p⁺-n junction and a metal electrode separated from the n-section of the p⁺-n junction by a semi-insulating (leaky) layer are presented. Two basic types of structure were studied: devices with relatively light doped n-sections, and those with relatively heavily doped sections.

The switching voltage of the first group was found to be proportional to the product of the doping density, N_d and the square of the width of the n-section, and to be only very weakly temperature-dependent. The capacitance-voltage relationship of the device in the high-impedance mode was found to be of the form C⁻¹ ∞ V^1/2, and these measurements established that switching occurred just as the depletion region of the n-section under the gate electrode reached through to the p⁺-n junction. It was thus established that these devices were operating in the punch-through mode.

In the second group of devices, the doping density of the n-section was increased by diffusing an n-well into the section. The switching properties were found to be quite different from the punch-through devices. The switching voltage was found to be independent of the width of the n-section and proportional to N_d^−3/4. Capacitance measurements also showed that the depletion region in the n-section under the oxide at switching, varied with the doping concentration, and was substantially less than the width of the n-layer. It was thus concluded that switching in these devices was of the avalanche-mode type.     

Quantized conductance in a Si/Si0.7Ge0.3 split-gate device and impurity-related magnetotransport phenomena

We have defined a quantum point-contact by the split-gate technique in a Si/SiGe heterostructure containing a two-dimensional electron gas with an elastic mean free path of about 1.3 μm. The conductance of this device shows typical steps very close to multiples of 4e² h⁻¹. Upon application of a perpendicular magnetic field the spin and valley degeneracies are lifted and magnetic depopulation of the one-dimensional subbands can be observed. The appearance of Aharonov-Bohm oscillations for B ≥ 2T and of resonant tunneling peaks close to “pinch-off” indicates the presence of impurities close to the constriction.     

An investigation of LixNi1−x,O as a mixed-valence thermoelectric material

The mixed valence material, Li_xNi_1−xO, has been investigated as a potential thermoelectric material. Measurements of the Seebeck coefficient, (μ V/°C), electrical resistivity, ρ(Ω-cm), and thermal conductivity, k(W/cm°C) have been made as a function of temperature and lithium concentration. The thermoelectric figure of merit, Z(²/ρk), reaches a value of approximately 1·4×10⁻⁴ at 1100°C for the composition Li_0.04Ni_0.96O.     

Investigation into the effect of Auger recombination on charge carrier transport and static characteristics of silicon multilayer structures

A new model for charge carrier transport through a silicon multilayer structure at high current density is presented. This model accounts for a number of nonlinear physical phenomena (electron-hole scattering, Auger recombination, high doping effects) which become of significance at high current density.

The injected charge carrier distribution in the lightly doped layer of the structure at high current density was investigated on the basis of this model and previously predicted phenomenon of injected carrier saturation is confirmed. The dependence of injected carrier limiting density on the electrophysical parameters of the silicon structure was investigated.

Within the framework of the suggested model the current-voltage characteristics of a p⁺-n-n⁺ structure was studied. It is demonstrated that injected carrier saturation phenomenon results in linear current-voltage characteristics at high current densities.

A characteristic ratio (W/L)_c (where W is the width of the n-base layer and L is the ambipolar diffusion length of charge carriers in the n-base layer) was found to divide the diode structures into two groups. In the first group with W/L<(W/L)_c the recombination of injected carriers in the n-base layer at high current density is provided by Auger processes only and therefore the current-voltage characteristics does not depend on lifetime τ, conditioned by the Shockley-Read-Hall recombination processes. The second group of structures with W/L>(W/L)_c retains a dependence on τ at all current densities.

Experimental data presented in the last section of the article confirm the results of device modeling.     

Interface characteristics of Ge3N4-(n-type) GaAs MIS devices

Passivation of GaAs surfaces was achieved by the deposition of Ge₃N₄ dielectric films at low temperatures. Electrical characteristics of MIS devices were measured to determine the interface parameters. From C-V-f and G-V-f measurements, density of interface states has been obtained as (4–6)×10¹¹ cm⁻² eV⁻¹ at the semiconductor mid-gap. Some inversion charge buildup was seen in the C-V plot although the strong inversion regime is absent. Thermally stimulated current measurements indicate a trap density of 5×10¹⁸−10¹⁹ cm⁻³ in the dielectric film, with their energy level at 0.59 eV.     

Analysis of I–V measurements on PtSi-Si Schottky structures in a wide temperature range

I–V Measurements on PtSi-Si Schottky structures in a wide temperature range from 90 to 350 K were carried out. The contributions of thermionic-emission current and various other current-transport mechanisms were assumed when evaluating the Schottky barrier height Φ₀. Thus the generation-recombination, tunneling and leak currents caused by inhomogeneities and defects at the metal-semiconductor interface were taken into account.

Taking the above-mentioned mechanisms and their temperature dependence into consideration in the Schottky diode model, an outstanding agreement between theory and experiment was achieved in a wide temperature range.

Excluding the secondary current-transport mechanisms from the total current, a more exact value of the thermionic-emission saturation current I_te and thus a more accurate value ofΦ_b was reached.

The barrier height Φ_b and the modified Richardson constant A^** were calculated from the plot of thermionic-emission saturation current I_te as a function of temperature too. The proposed method of finding Φ_b is independent of the exact values of the metal-semiconductor contact area A and of the modified Richardson constant A^**. This fact can be used for determination of Φ_b in new Schottky structures based on multicomponent semiconductor materials.

Using the experimentally evaluated value A^** = 1.796 × 10⁶ Am⁻²K⁻² for the barrier height determination from I–V characteristics the value of Φ_b = 0.881 ± 0.002 eV was reached independent of temperature.

The more exact value of barrier height Φ_b is a relevant input parameter for Schottky diode computer-aided modeling and simulation, which provided a closer correlation between the experimental and theoretical characteristics.     

Simulation and analysis of amorphous silicon image sensor having a p−i−n structure

The current-voltage characteristics of a p−i−n a-Si : H contact image sensor under dark and illuminated conditions have been simulated by solving the Poisson's equation and the continuity equations, and the results are correlated with the experiments. The dependence of the dark and photo-currents on the parameters such as the density of states in the gap, intrinsic layer width, dopant concentrations of p⁺ layer and n⁺ layer are discussed.     

Metal-insulator transition in Sb-doped short period Si/SiGe superlattices

Low-temperature magnetotransport measurements (50 mK < T < 4.2 K) on Sb-doped short period Si/SiGe superlattices (d ≈ 40 Å) are presented. The experiments show evidence for single particle quantum interference and enhanced electron-electron interaction effects. Furthermore, for a Sb doping concentration of 4.5 × 10¹⁸ cm⁻³, a field induced metal to insulator transition (MIT) is observed for magnetic fields B parallel to the superlattice layers, whereas for the perpendicular direction of B, the MIT does not take place. The anisotropy and dimensionality of the SL-samples is discussed.     

Theory of open circuit photo-voltage in degenerate abrupt p-n junctions

In this paper we have presented a comprehensive theory of photovoltage in degenerate abrupt p-n junction. In contrast to the earlier work[9], we use a generalized diffusion-mobility relation for charge carriers which is valid for extreme degeneracy. The general expression for the photo e.m.f. is used to obtain explicit expression for the case of lowinjection levels for two types of p−n junction. (i) When both the neutral regions are extremely degenerate and (ii) when one region is extremely degenerate but other is non-degenerate. Some numerical results of photo e.m.f. for typical p⁺n and n⁺p junctions are presented.     

Carrier recombination in single crystal PbSe

The photoconductivity decay curves after illumination of single crystal n- and p-type PbSe were analysed assuming recombination through different localized impurity levels in conjunction with direct recombination. The lifetimes deduced for direct (Auger and radiative) recombination below 250 K were in agreement with the calculated values for carrier concentrations 2·10¹⁷ cm⁻³. Furthermore, the existence of up to three impurity levels was concluded from the longer lifetime-components present in the decay curves. Appropriate approximations of the general recombination theory yielded energies separated between 20 and 50 meV from the nearer band edge and minority carrier cross sections 10⁻¹⁷−4·10⁻¹⁹ cm² in the temperature range 250-100 K, and majority carrier cross sections 10⁻¹⁹−10⁻²⁰ cm² at T < 100 K for these levels.     

Magneto-optical studies of the type I/type II crossover and band offset in ZnTe/Zn1−xMnxTe superlattices in magnetic fields up to 45 T

We report measurements of magneto-reflectivity in ZnTe/Zn_1−xMn_xTe superlattices in magnetic fields up to 45 Tesla. From an analysis of the Zeeman splitting, we investigate the change of band alignment with field and the band offset ratio. A crossing of the 1 s exciton transitions from the ZnTe buffer layer and the 1 s heavy hole σ₊ exciton of the superlattice is observed, providing unambiguous evidence of a band alignment change from type I to type II. The excitonic energy levels for both type I and type II band structure are calculated using a variational method. This model fits the experimental data very well at high field for both σ₊ and σ₋ transitions. A conduction band offset ratio of ΔE_c/ΔE_s=0.72±0.04 is deduced.     

Determination of the LO-phonon and Γ→L intervalley scattering time in GaAs from hot electron luminescence spectroscopy

Both the LO-phonon scattering time and the Γ→L intervalley scattering time for electrons in the conduction band of GaAs are of fundamental importance, and they are needed for the modelling of devices. We measure the steady state distribution of hot electrons in lightly p-doped bulk GaAs under carrier densities of 10¹³–10¹⁴cm⁻³, which is orders of magnitude lower than in pulsed laser experiments. Using a 16×16 k.p Hamiltonian and taking into account the transition matrix elements in a dipole model, we determine the hot electron lifetime from comparison with the experimentally found lifetime broadening. For electrons with a kinetic energy of 100meV to 300meV we obtain τ_LO=(132±10)fs. We also determine the Γ→L intervalley separation as E_ΓL=(300±10)meV. We find Γ→L scattering times around 150fs to 200fs, corresponding to a value for the associated deformation potential of D_ΓL=(9.4±1.5)×10⁸eV/cm.     

Effect of junction depth on the performance of a diffused np silicon solar cell

A detailed numerical analysis of the influence of the junction depth on the performance of a diffused n⁺p silicon solar cell is presented. The analysis includes the effects of Fermi-Dirac statistics, band gap narrowing, a finite surface recombination velocity and the built-in field due to the impurity profile. The recombination mechanism plays a dominant role in the performance of the solar cell. The ideality factor, “a”, varies from 1.006 for 0.1 μm junction depth, to 1.0135 for 2 μm junction depth. The saturation current density, J_o increases with the junction depth showing that the recombination increases in the heavily doped diffused layer of the device. The variation of the light generated current, J_L, the open-circuit voltage, V_oc, efficiency, η and the ideality factor, “a” are reported and analysed.     

100 Å-thick tunnel junction by double impurity doping liquid phase epitaxy for V-band TUNNETT oscillation

The tunnel injection transit time (TUNNETT) diodes with p⁺p⁺n⁺n⁻n⁺ structure were fabricated by liquid phase epitaxy (LPE). About 100 Å tunnel junction (p⁺n⁺) was successfully prepared by the double impurity diffusion of Ge and S during LPE growth. Continuous wave (CW) oscillation was realized at 51.520 GHz in the V-band cavity with the phase noise of −60 dBc/Hz at 1 kHz bandwidth.     

Effect of collector design on the d.c. characteristics of In0.49Ga0.51P/GaAs heterojunction bipolar transistors

InGaP/GaAs heterojunction bipolar transistors with various collector structures are compared. The dependence of d.c. device characteristics on the thickness of the n⁻ GaAs spacer in the collector of composite collector devices is presented. Results indicate that the spacer thickness significantly affects the performance of the transistor. An n⁺ doping spike on the InGaP side of the collector heterojunction is included in the collector design of the composite collector devices. Standard single-heterojunction d.c. results are compared to abrupt double- and composite collector heterojunction devices. Optimization of the spacer thickness, in conjunction with the n⁺ doping spike, eliminates most of the detrimental effects associated with a double-heterojunction device while retaining the beneficial properties of a wide-gap collector. As expected, the composite collector structure produces devices with higher breakdown voltages and lower offset voltages than single heterojunction devices. In addition, optimizing the spacer thickness can reduce the collector current saturation voltage of the composite collector device below that of a single-heterojunction device. These characteristics make composite collector heterojunction bipolar transistors ideal candidates for high power microwave device applications.     

Estimation for the capture cross-sections of surface state on p-Si surface by photovoltaic method

A new method which can nondestructively measure the surface-state density (SSD) D_s and estimate the capture cross-sections (CCS) of surface state σ⁰_n and σ⁻_p on surface of p-type semiconductor crystals is proposed. This method is based on the photovoltage measurements at various temperatures. The photovoltage experiment was carried out with a (1 1 1) p-type Si single crystal (N_A=4.8×10¹⁴ cm ⁻³). Owing to that the surface barrier height φ_BP=0.6421 V and the surface-recombination velocity s_n=9.6×10³ cm s⁻¹ of this sample can be determined, the SSD D_s=1.2×10¹¹ cm⁻² eV⁻¹ can therefore be obtained, furthermore CCS σ⁰_n≈5×10⁻¹⁴ cm² and σ⁻_p≈2×10⁻¹⁰ cm² can also be estimated. These results are consistent with that of related reports obtained by other methods.