Temperature dependence of impact ionization in GaAs

The temperature dependence of electron and hole impact ionization in gallium arsenide (GaAs) has been determined from photomultiplication measurements at temperatures between 20 K and 500 K. It is found that impact ionization is suppressed by increasing temperature because of the increase in phonon scattering. Temperature variations in avalanche multiplication are shown to decrease with decreasing avalanching region width, and the effect is interpreted in terms of the reduced phonon scattering in the correspondingly reduced ionization path length. Effective electron and hole ionization coefficients are derived and are shown to predict accurately multiplication characteristics and breakdown voltage as a function of temperature in p/sup +/in/sup +/ diodes with i-regions as thin as 0.5 /spl mu/m.     

Hot electron transport in wurtzite-GaN: effects of temperature and doping concentration

The hot electron transport in wurtzite phase gallium nitride (Wz-GaN) has been studied in this paper.An analytical expression of electron drift velocity under the condition of impact ionization has been developed by considering all major scattering mechanisms such as deformation potential acoustic phonon scattering,piezoelectric acoustic phonon scattering,optical phonon scattering,electron-electron scattering and ionizing scattering.Numerical calculations show that electron drift velocity in Wz-GaN saturates at 1.44 x 105 m/s at room temperature for the electron concentration of 1022 m-3.The effects of temperature and doping concentration on the hot electron drift velocity in Wz-GaN have also been studied.Results show that the saturation electron drift velocity varies from 1.91 × 105-0.77 × 105 m/s for the change in temperature within the range of 10--1000 K,for the electron concentration of 1022 m-3;whereas the same varies from 1.44 x 105-0.91 × 105 m/s at 300 K for the variation in the electron concentration within the range of 1022-1025 m-3.The numerically calculated results have been compared with the Monte Carlo simulated results and experimental data reported earlier,and those are found to be in good agreement.     

Electrical characterization of high purity InGaAsP alloys

In_xGa_1-xAs_yP_1-y layers grown by liquid phase epitaxy on InP substrates were characterized by Hall effect between 4 and 300K. The thermal activation energy of donor impurities was estimated from the temperature dependence of the free electron concentration ; it was found to increase with phosphorus concentration from less than 1meV in InGaAs to about 2.5meV in InP. Evidence for impurity conduction was also observed in some samples at the lowest temperatures. The mobility analysis led to an estimation of the alloy scattering potential in the whole range of compositions 0≤y≤l. At temperatures below 10K, we observed avalanche effect due to impact ionization of electrons from shallow donor impurities into the conduction band.     

DC performance of deep submicrometer Schottky-gated n-channel Si:SiGe HFETs at low temperatures

N-type Schottky-gated Si:SiGe heterostructure field-effect transistors with physical gate lengths between 70 and 450nm are characterized over a wide temperature range (T=10 K...300 K) for low electric fields. The room-temperature maximum low-field transconductance increases 61% to 440 mS/mm at T=10 K for the 70-nm device. The minimum subthreshold slope is 14...19 mV/dec at T=10 K. The off-state currents I/sub OFF/ are limited by parallel conduction at high temperatures and by the gate leakage current at low temperatures. Substrate leakage currents are found to be due to generation of carriers within the drain/substrate depletion layer and only make a minor contribution to I/sub OFF/. Operation of the devices at the lowest temperature is found to result in the occurrence of the floating-body kink effect, as a consequence of substrate freeze-out and subsequent self-biasing by impact ionization currents. Low temperature characteristics exhibit a nonlinear low-field drain current dependence on the drain voltage, due to the presence of parasitic Schottky source/drain contacts. An extraction method for access resistance consistent with this phenomenon is presented.     

Avalanche multiplication in InP/InGaAs double heterojunctionbipolar transistors with composite collectors

The experimental and theoretical studies of electron multiplication in InP/InGaAs double heterojunction bipolar transistors (DHBT's) with an InGaAs/InP composite collector are carried out. Both local electric field model and energy model are used to investigate the electron impact ionization in the composite collector. The analysis reveals that the nonlocal effect of the electron impact ionization in the composite collector is responsible for the suppression of the contribution of electron multiplication in the InGaAs layer. Experimental results for the fabricated devices were compared with the theoretical calculations, indicating that the conventional impact ionization models based on the local electric field significantly overestimate the electron multiplication for the composite collector. The energy model which takes into account the nonlocal effect is found to provide a more accurate prediction of electron multiplication for the DHBT's     

Temperature dependence of InGaP/GaAs heterojunction bipolartransistor DC and small-signal behavior

This work describes the temperature dependence of the DC and small-signal performance of InGaP/GaAs heterojunction bipolar transistors (HBT's) with different collector thicknesses. Detailed analyses of the small-signal performance and the temperature dependence of both DC and high-frequency parameters are presented. An HBT delay-time analysis is also presented and justified empirically. In addition, the factors causing the decrease in f_T with temperature are described, and the variations in collector resistance and collector drift velocity with temperature are determined     

Temperature dependence of avalanche multiplication in InP-based HBTs with InGaAs/InP composite collector: device characterization and physics model

Recent efforts are being focused on improving the breakdown of InP-based heterojunction bipolar transistors (HBTs) towards high-power applications. A fundamental understanding of the temperature dependence of breakdown and its physics mechanism in these devices is important. In this work, a detailed characterization of temperature-dependent collector breakdown behavior in InP DHBTs (DHBTs) with an InGaAs/InP composite collector is carried out. A physics model for the prediction of temperature-dependent breakdown in lnP/InGaAs composite collector is developed. We found that, although the variation of impact ionization coefficient due to the change of temperature may affect the device breakdown, the temperature-dependence of breakdown in the lnGaAs/InP composite collector could be significantly affected by the carrier transport in the InGaAs region. As temperature is increased, the increase in the contribution of InGaAs layer to the junction breakdown due to the reduction of electron energy relaxation length could be the root cause of the reduction of junction breakdown voltage. Good agreement between the physics model and experimental data demonstrate the validities of the proposed physics model to predict the temperature dependent breakdown characteristics for InP DHBTs.     

Temperature dependence of hot-electron-induced degradation in MOSFET's

The temperature dependence of MOSFET degradation due to hot-electron injection has been studied. The slower degradation rate at elevated temperature at fixed stressing bias follows the substrate current level which is reduced mainly by lower localized electric field rather than lower ionization coefficient (both are caused by enhanced phonon scattering). The actual degradation rate at the constant substrate current level is slightly higher at elevated temperatures, indicating an enhanced interface-state generation mechanism. This temperature dependence provides a simple relationship between device degradation and substrate current at various temperatures.     

MOS device modeling at 77 K

The state of the art in self-consistent numerical low-temperature MOS modeling is reviewed. The physical assumptions that are required to describe carrier transport at low ambient temperatures are discussed. Particular emphasis is placed on the models for space charge (impurity freeze-out), carrier mobility (temperature dependence of scattering mechanisms at a semiconductor-insulator interface), and carrier generation-recombination (impact ionization). The differences with regard to the numerical methods required for the solution of low-temperature models compared to room-temperature models are explained. Typical results obtained with the simulator MINIMOS 4 are presented. These include comparisons of short-channel effects and hot-electron phenomena such as energy relaxation and avalanche breakdown at 77 K and 300 K ambient temperatures     

Interplay of geometric and electronic structure in thin films of diindenoperylene on Ag(1 1 1)

Using the example of Diindenoperylene (DIP) a strong dependence of ionization potential, electron affinity and transport gap on the growth conditions of an organic molecular thin film is demonstrated. DIP single crystals show a remarkable polymorphism as single crystals as well as crystalline films on weakly interacting substrates like Au or SiO₂ surfaces. We have investigated DIP thin films on Ag(1 1 1) substrates and found a strong dependence of the photoemission and inverse photoemission spectra as well as of the low energy electron diffraction (LEED) patterns on the substrate temperature. Three different temperature regions could be identified with distinct reproducible signatures in the structural data as well as in the valence level spectra. Peak positions, line widths, and relative intensities directly correlate with the degree of order and with the molecular orientation. Moreover, we identified a systematic change of the structural quality ranging from high mosaicity at low temperature (<150 K) via small ordered domains (150–250 K) to a high degree of order at elevated temperature (>350 K).     

Autosolitons in bistable system of silicon with deep impurity levels

Autosolitons in the bistable system of silicon associated with the thermal and electric-field ionization of In deep acceptor levels at a temperature of 77 K are experimentally found and investigated. It is shown that the positive feedback on the activator is related in the considered model of autosolitons to an increasing dependence of the lattice temperature on growth in the hole concentration, while the damping role of the inhibitor is associated with a decrease in the charge-carrier temperature during phonon-induced scattering. This leads to power-loss reduction and lattice-temperature restriction in the vicinity of autosolitons.     

Temperature dependence of the anomalous leakage current inpolysilicon-on-insulator MOSFET's

A new analytical model is presented for the temperature and bias dependence of the anomalous leakage current based on thermionic field emission via grain boundary traps in the gate-drain overlap region in polysilicon-on-insulator MOSFET's. The existing model based on pure field emission (tunneling) via grain boundary traps does not include a temperature dependence and therefore cannot explain the observed strong temperature dependence of leakage at low gate voltages, as well as the weaker temperature dependence at high gate voltages, which the new analytical model presented in this paper can. Below 150 K, we believe that impact ionization due to the increasing carrier mean free path leads to the observed increase in the leakage current with decreasing temperature. Since the analytical model does not include impact ionization, it cannot model the leakage current at low temperatures     

Measurements of InGaP electron ionization coefficient using InGaP-GaAs-InGaP double HBTs

Electron impact ionization coefficients (/spl alpha/) in In/sub 0.52/Ga/sub 0.48/P have been extracted based on the measurements of electron multiplication factor in npn InGaP-GaAs-InGaP double heterojunction bipolar transistors (HBTs). The electron ionization coefficient of InGaP determined in this brief extends the previously reported data in low electric field by two orders of magnitude down to 1 cm/sup -1/ with the electric field as low as 330 kV/cm.     

Temperature dependence of 1/f noise in polysilicon-emitter bipolar transistors

1/f noise was measured on polysilicon-emitter bipolar n-p-n and p-n-p transistors over a temperature range of 173K相似文献   

Influence of the interface-state density on the electron mobility in silicon inversion layers

The electron inversion-layer mobility in a metal oxide semiconductor field effect transistor, as a function of the transverse electric field, has been studied in the temperature range 13–300K for different interface-state densities. Experimental data are in excellent agreement with a simple semi-empirical model. However, the term attributed by other authors to phonon scattering depends on the interface-state density, even at high temperatures, and becomes negative at low temperatures. These facts are shown to be a consequence of the dependence of coulomb scattering on the transverse electric field.     

Electrical properties and transport mechanisms of InP/InGaAs HBTsoperated at low temperature

The electrical properties of InP/InGaAs HBTs have been comprehensively investigated between room and near liquid helium temperature. Physical mechanisms for the devices operated in different temperature ranges have been clearly identified. The low temperature measurements indicate that, in the temperature range of 240 K to 300 K, the base current is dominated by electron-hole band-to-band recombination; in the temperature range 77 K to 240 K, trap-related recombination (Shockley-Read-Hall recombination) plays an important role in determining base current; and for temperature lower than 77 K, the collector and base currents are found to be limited by electron tunneling through the barrier formed by the conduction-band discontinuity at the E-B junction. These findings provide us with better physical insight of the device operation at low temperature, which is particularly important for the optimization of InP HBT technology for low temperature applications as well as the development of a quantitative model for circuit design     

Impact ionization and real-space transfer of minority carriers incharge injection transistors

High electric fields in the channel of InGaAs-InAlAs heterostructure complementary charge injection transistor give rise to impact ionization and real-space transfer of minority holes from the channel. These phenomena are investigated by measuring light emission in the 1.1-3.1 eV energy range for different points on the electrical characteristics. The effective carrier temperature, determined from the exponential tails of electroluminescence spectra, is 2100 K in the channel and 450 K in the barrier     

Monte Carlo simulation of impact ionization in SiGe HBTs

Measurements and Monte Carlo simulations of impact ionization in the base-collector region of SiGe HBTs are presented. A device with low germanium concentration (graded from 0 to 12%) is considered and no differences are found between the experimental multiplication factor in that device and the corresponding silicon control. Because impact ionization (II) occurs inside the bulk-Si collector, phonon and II scattering rates for bulk silicon can be used in the Monte Carlo simulation, avoiding the need to model the strained SiGe layers. Full-Band Monte Carlo simulations are shown to reproduce the multiplication factors measured in SiGe devices featuring different collector profiles     

Normalized theory of impact ionization and velocity saturation in nonpolar semiconductors via a Markov chain approach

This paper presents an investigation of the velocity, energy, and impact ionization distributions in nonpolar semiconductors at very high fields. The treatment uses a finite Markov chain formulation. When optical phonon collisions and impact ionization are the major scattering mechanisms in the semiconductor, a transition matrix which characterizes the transition probabilities between virtual states defined by small discrete energy intervals can be easily computed. The resulting matrix provides the means not only to study the impact ionization phenomenon but also the steady state transport velocity and energy distribution of the charge carriers at high electrical fields and a given lattice temperature. In addition, the effects on the transport properties due to either an abrupt infinite (AI) or a finite energy dependent (FED) ionization cross-section above the ionization threshold energy are examined. The calculated avalanche transport velocity shows excellent agreement with the experimental data in Si obtained by Duh and Moll. The resulting calculations when extrapolated to a lower field also agree favorably with existing saturation drift velocity data in n and p type Si and p type Ge. The energy distribution is shown to be strongly affected by the choice of the model for the energy dependence of the ionization cross-section. One of the main applications of the results is to assist investigation of the non-localized nature of electron and hole avalanche ionization coefficients previously noted by Okuto and Crowell (O-C). The present results for this spatial distribution can replace O-C's intuitively chosen exponential approximation. The spatial ionization distribution generated by the present calculation is essentially exponential with a threshold energy dark space. This result provides a useful kernel for a more precise formulation in studies that relate impact ionization coefficients to charge multiplication data. The normalized ionization coefficients obtained from the AI model are very similar to Baraff's calculation as are the FED model results after appropriate normalization. Simple analytical expressions with meaningful asymptotic results for the average ionization energy and the ionization coefficient are also derived from the present data. These results are applicable for a range of different energy dependence of the ionization cross section provided that the average energy for pair production is used as the effective threshold parameter.     

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.