Thermal noise of a silicon double-injection plasma diode

Measurements of the thermal noise of a silicon p⁺−π−n⁺ diode operating in the Lampert-insulating regime agree within 6 per cent with the prediction S_i = 4kT Re(Y). The noise measurements were performed in the cube-law regime with d.c.-currents from 100 μA to 4mA at room temperature.     

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.     

Breakdown voltage of diffused epitaxial junctions

The quantitative aspects of the breakdown-voltage calculations in reach-through-limited p⁺−n−n⁺ junctions are revisited, using numerical simulation. It is shown that the conventional abrupt-junction approximation may underestimate the breakdown voltage of diffused epitaxial junctions by as much as 60%, depending on junction depth. Oppositely, but less erroneously, a combined abrupt/linearly-graded approximation overestimates the breakdown voltage by at most 15%. A set of numerically calculated plots are provided for the design of low-voltage power devices.     

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.     

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.     

Numerical simulation of temperature-dependent minority-hole transport in n silicon emitters

A one-dimensional numerical computer simulation of minority-hole transport in heavily doped n⁺ silicon emitters is developed accounting for significant temperature dependences. The model includes the most recent insights regarding heavy-doping effects, which indeed facilitate the accounting for the temperature dependences. Measurements of base current in polysilicon-contacted n⁺pn transistors over a wide temperature range, carefully interpreted by accounting for unavoidable device/ambient temperature discrepancies, support the model and demonstrate its utility, for example in characterizing the electrical properties of the polysilicon emitter contact.     

Lateral tunneling transistors fabricated by plane-dependent Si-doping in nonplanar epitaxy on GaAs (311)A and (411)A substrates

We have demonstrated the lateral tunneling transistors on GaAs (311)A and (411)A patterned substrates by using the plane-dependent Si-doping technique. Lateral p⁺-n⁺ tunneling junctions are formed by growing heavily Si-doped layers on patterned substrates. Current—voltage curves for both transistors show gate-controlled negative differential resistance characteristics. Furthermore, the peak current density of the lateral tunneling diodes fabricated on the (311)A patterned substrates increases as buffer layer thickness is increased, and a typical peak current density of 58 A/cm² for p = 6 × 10¹⁹ cm⁻³ and n = 7 × 10¹⁸ cm⁻³ is obtained when the buffer layer thickness is 1.2 μm. This study shows that plane-dependent Si-doping in non-planar epitaxy is a promising technique for fabricating tunneling transistors.     

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.     

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.     

Modeling of the hot electron subpopulation and its application toimpact ionization in submicron silicon devices-Part II: numericalsolutions

A macroscopic transport model for the hot electron subpopulation (HES) and a nonlocal impact ionization (II) model were proposed in Part I of this article: see ibid. p. 1200, 1994. The transport equations have been derived from the Boltzmann transport equation (BTE) and closure has been provided by an empirically determined equation. The transport equations and the II model have been calibrated using data obtained from self-consistent Monte Carlo (SCMC) simulations. In this article we present the numerical solutions obtained by applying the proposed model to n⁺- n^--n⁺ structures with various doping profiles. The results are compared to the data obtained from SCMC simulations and also to those obtained from models proposed earlier by other authors     

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.     

Nitrogen vacancy scattering in GaN grown by metal–organic vapor phase epitaxy

Electron mobility limited by nitrogen vacancy scattering was taken into account to evaluate the quality of n-type GaN grown by metal–organic vapor phase epitaxy. Two assumptions were made for this potential for the nitrogen vacancy (1) it acts in a short range, and (2) does not diverge at the vacancy core. According to the above assumptions, a general expression to describe the scattering potential U(r)=−U₀exp[−(r/β)ⁿ], (n=1,2,…,∞) was constructed, where β is the potential well width. The mobilities for n=1,2, and ∞ were calculated based on this equation, corresponding to the simple exponential, Gaussian and square well scattering potentials, respectively. In the limiting case of kβ1 (where k is the wave vector), all of the mobilities calculated for n=1,2, and ∞ showed a same result but different prefactor. Such difference was discussed in terms of the potential tail and was found that all of the calculated mobilities have T^−1/2 temperature and β⁻⁶ well width dependences. A mobility taking account of a spatially complicate scattering potential was studied and the same temperature dependence was also found. A best fit between the calculated results and experimental data was obtained by taking account of the nitrogen vacancy scattering.     

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.     

Ohmic contacts for GaAs devices

Contact alloys were developed for use on a wide variety of GaAs devices such as high temperature transistors and Gunn oscillators. The alloys are composed of silver, indium and germanium for n-type GaAs and of silver, indium and zinc for p-type GaAs. Fabrication steps that require temperatures of up to 770°K for already contacted devices can be performed. GaAs transistors can be operated over a range from 20 to 770°K using Ag-In-Ge contacts for emitter and collector and Ag-In-Zn contacts for the base. Gunn oscillators have been built for the frequency range between 13 and 26 GHz with efficiencies as high as 3 percent at 15.8 GHz and as high as 1 percent at 25 GHz in continuous wave operation. A simple technique was developed to evaluate the specific contact resistance on thin epitaxial layers. Specific contact resistance is well below 10⁻⁴ ω-cm² on 0.1 ω-cm or lower resistivity p- or n-type GaAs. The highest value was 1 × 10⁻³ ω-cm² measured on 0.6–2.6 ω-cm n-type GaAs.     

n-Channel AlSb/GaSb modulation-doped field-effect transistors

We report the first fabrication of a GaSb n-channel modulation-doped field-effect transistor (MODFET) grown by molecular beam epitaxy. The modulation-doped structure exhibits a room temperature Hall mobility of 3140 cm² V⁻¹ s⁻¹ and 77 K value of 16000 cm² V⁻¹ s⁻¹, with corresponding sheet carrier densities of 1.3 × 10¹² cm⁻² and 1.2 × 10¹² cm⁻². Devices with 1 μm gate length yield transconductances of 180 mS mm⁻¹ and output of 5 mS mm⁻¹ at 85 K. The device characteristics indicate that electron transport in the channel occurs primarily via the L-valley of GaSb above 85 K. The effective electron saturation velocity is estimated to be 0.9 × 10⁷ cm s⁻¹. Calculations show that a complementary circuit consisting of GaSb n- and p-channel MODFETs can provide at least two times improvement in performance over AlGaAs/GaAs complementary circuits.     

Transport of the photoexcited electron-hole plasma in InP

Transport properties of the photoexcited electron-hole plasma in n-type InP have been studied by the spatial-imaged, time-resolved Raman scattering technique with 30μm and 0.1μm spatial resolution for lateral and perpendicular transport, respectively, and on a picosecond time scale. The plasma density ranging from 1 × 10¹⁶ to 2 × 10¹⁷ cm⁻³ was deduced from fitting of the Raman spectra with the plasmon-LO phonon scattering theory which took into account the contributions from free holes. In contrast to the experimental results of Young and Wan who found that ordinary diffusion equation was sufficient to fit their transient plasma density-time profiles in semi-insulating InP, our experimental measurements have shown that perpendicular transport (i.e., expansion into the bulk crystal) of the plasma in n-type InP can be very well described by a modified diffusion equation including the effect of drifting away from the surface based on a hydrodynamic model. The transient plasma density-time profiles were studied at T = 300K and for an initial injected plasma density n 2 × 10¹⁷ cm⁻³. The plasma has been found to expand laterally at a velocity V 5 × 10⁴ cm/sec and perpendicularly into the crystal at a velocity Vp 1.5 × 10⁵ cm/sec.     

Schottky barrier height of a new ohmic contact NiSi2 to n-type 6H-SiC

We present a new ohmic contact material NiSi₂ to n-type 6H-SiC with a low specific contact resistance. NiSi₂ films are prepared by annealing the Ni and Si films separately deposited on (0 0 0 1)-oriented 6H-SiC substrates with carrier concentrations (n) ranging from 5.8×10¹⁶ to 2.5×10¹⁹ cm⁻³. The deposited films are annealed at 900 °C for 10 min in a flow of Ar gas containing 5 vol.% H₂ gas. The specific contact resistance of NiSi₂ contact exponentially decreases with increasing carrier concentrations of substrates. NiSi₂ contacts formed on the substrates with n=2.5×10¹⁹ cm⁻³ show a relatively low specific contact resistance with 3.6×10⁻⁶ Ω cm². Schottky barrier height of NiSi₂ to n-type 6H-SiC is estimated to be 0.40±0.02 eV using a theoretical relationship for the carrier concentration dependence of the specific contact resistance.     

Hydrodynamic hot-electron transport simulation based on the Monte Carlo method

A hydrodynamic hot electron model is used to study electron transport through a submicron N⁺ --- N --- N⁺ GaAs structure. This study is used to investigate improvements which the unique features of this model offer to analysis of devices operating under nonstationary transport conditions. The model is based upon semiclassical “hydrodynamic” conservation equations for the average carrier density, momentum and energy. The general model includes particle relaxation times, momentum relaxation times, energy relaxation times, electron temperature tensors and heat flow vectors as a function of average carrier energy for the Γ, X and L valleys of GaAs. For this study, we utilized a simplified single electron gas version of our model to clearly reveal the impact of the nonstationary terms in the model. Results from both a drift-diffusion model approach and a Monte Carlo analysis are used to show the relative accuracy and facility this new model offers for investigating practical submicron device structures operating under realistic conditions.     

Theory of back surface field silicon solar cells

Back surface field silicon solar cells with n⁺pp⁺ (or sometimes p⁺nn⁺) structures are found to have better characteristics than the conventional solar cells. The existing theories have not been able to satisfactorily predict the experimentally observed parameters on these cells. A theory, based on the transport of both minority and majority carriers under the charge neutrality condition, has been developed in the present paper which explains the behavior of the back surface field solar cells. Good agreement is achieved between the results obtained by using this theory and the experimental observations of earlier workers.