Transient electronic transport in InP under the condition of high-energy electron injection

Transient transport of electrons in InP is studied under the condition of high-energy electron injection. This study makes use of a Monte Carlo simulation with the unique inclusion of realistic band-structure as derived from an empirical pseudopotential method. The results obtained herein for InP are qualitatively similar to those previously obtained by the authors for GaAs. Quantitatively, it is found that ultra-high electron drift velocities (≈10⁸cm/s) persist for much higher electric fields and over much longer distance of electron traversal in InP as compared to GaAs.     

A large enhancement of the maximum drift velocity of electrons in the channel of a field-effect heterotransistor

It is shown that the optical-phonon momentum quantization in a GaAs quantum well resulting from the introduction of an InAs quantum-dot barrier layer provides for the elimination of inelastic scattering of electrons by optical phonons and, thus, makes the acceleration of electrons above the saturation drift velocity possible. It is shown experimentally that the maximum drift velocity of electrons in high electric fields in AlGaAs/GaAs heterostructure with InAs quantum-dot barriers introduced into the GaAs quantum well exceeds the saturation drift velocity in bulk GaAs by as much as a factor of 10. Such a rise in the maximum drift velocity of electrons ensures increased maximum current density, transconductance, and cutoff frequency of the heterostructure field-effect transistor with quantum dots.     

Electron drift velocity in GaAs using a variable frequency microwave time-of-flight technique

A modified form of microwave time-of-flight technique has been developed which uses a variable frequency microwave deflection system to modulate the electron beam. This enables electron drift velocities to be measured absoslutely over a wide range of values whereas previous microwave time-of-flight measurements have given only relative velocities and require at least one point of normalisation. This new technique has been applied to measure the drift velocity of electrons in n-type GaAs for electric fields up to 135 kV cm^?1 and over the temperature range 77–400 K. For fields above 10 kV cm^?1, excellent agreement is obtained with conventional time-of-flight measurements.     

A quantum-dot heterostructure transistor with enhanced maximum drift velocity of electrons

A new type of heterotransistor based on an AlGaAs/GaAs/InAs/GaAs/InAs structure with a layer of InAs quantum dots embedded directly into the GaAs channel is fabricated. High values of the maximum saturation current (up to 35 A/cm) and transconductance (up to 1300 mS/mm) are attained. The specific features of the current-voltage characteristics of the new device are explained in the context of a model that takes into account the ionization of quantum dots in high electric fields and tenfold enhancement of the electron drift velocity in a structure with an InAs quantum-dot layer in the vicinity of an AlGaAs/GaAs heterojunction.     

Effect of ionised impurity scattering on the electron transit time in GaAs and InP f.e.t.s

The effect of ionised impurity scattering on the transient drift velocity of electrons in short-gate GaAs and InP field-effect transistors is investigated by Monte Carlo techniques.     

Design and characteristics of InGaAs/InP composite-channel HFET's

A design for composite-channel structures consisting of an InGaAs channel and an InP subchannel for use as heterostructure field-effect transistors is presented for the first time. This novel channel structure takes advantage of both the high drift velocity and low impact ionization of InP at high electric fields as well as the high electron mobility of InGaAs at low electric fields. It is shown that the doping density of the InP subchannel is the key parameter to realize the advantages of the composite channel. A very high transconductance of 1.29 S/mm and a current gain cutoff frequency of 68.7 GHz are achieved with 0.6 and 0.7 /spl mu/m gates, respectively. The average velocity of electrons in the composite channel is 2.9/spl times/10/sup 7/ cm/s. The devices have no kink phenomena in their I-V characteristics possibly due to low impact ionization in the InP subchannel.<>     

InAs自组织生长量子点的电子俘获势垒

成功地用深能级瞬态谱（ＤＬＴＳ）研究了ＩｎＡｓ自组织生长的量子点电学性质，获得２．５原子层ＩｎＡｓ量子点电子基态能级在ＧａＡｓ导带底下约０．１３ｅＶ，该量子点在荷电状态发生变化时伴随有晶格弛豫，对应俘获势垒为０．３２ｅＶ．本工作也证明可以把量子点类比深中心进行研究．     

Reactive Ion Etching of GaAs, GaSb, InP and InAs in Cl2／Ar Plasma

Reactive ion etching characteristics of GaAs,GaSb,InP and InAs using Cl_2/Ar plasma have been investigated,it is that,etching rates and etching profiles as functions of etching time,gas flow ratio and RF power.Etch rates of above 0.45 μm/min and 1.2 μm/min have been obtained in etching of GaAs and GaSb respectively, while very slow etch rates (<40 nm/min) were observed in etching of In-containing materials,which were linearly increased with the applied RF power.Etched surfaces have remained smooth over a wide range of plasma conditions in the etching of GaAs,InP and InAs,however,were partly blackened in etching of GaSb due to a rough appearance.     

Electron dynamics in short-channel InP field-effect transistors

The transient response of electrons to a high field in InP has been calculated by a Monte Carlo method. The results are compared with previously published results for GaAs, and used to indicate the performance that may be obtained in InP and GaAs microwave f.e.t.s.     

Scattering of electrons by confined interface polar optical phonons in a double-barrier heterostructure

It is shown that capture of the surface (interface) phonons can occur in a double-barrier heterostructure in addition to the capture of bulk polar optical phonons. The strength of interaction of electrons with confined interface phonons becomes lower as the thickness of the phonon well (a semiconductor layer where phonons are captured) is decreased. A new approach is suggested for reducing the scattering of electrons by polar optical phonons in a double-barrier quantum well; this approach is based on separate capture of phonons in narrow phonon wells. The calculated scattering rate with the capture of interface phonons into the GaAs/InAs/GaAs and AlAs/GaAs/AlAs quantum wells taken into account is found to be much lower than the rate obtained in the approximation of scattering of electrons by bulk phonons. A multifold decrease in the rate of electron-phonon scattering in the AlAs/GaAs/AlAs quantum well is obtained by separating this well by the monomolecular InAs layer that is transparent for electrons but acts as a reflecting barrier for polar optical phonons.     

Calculated electron and hold spatial ionization profiles in bulkGaAs and superlattice avalanche photodiodes

The author presents ensemble Monte Carlo calculations of the electron and hole spatial and temporal impact ionization profiles in bulk GaAs and GaAs-AlGaAs superlattice structures. The results indicate that transient effects are much more pronounced for electrons than for holes, which greatly influences the dynamics of each type. It is concluded that the heterointerface plays less of a role in the hole ionization process than that for electrons due to the small valence band edge discontinuity and to the weaker nonlinear, transient effects experiences by the holes     

Indirect band gaps in quantum dots made from direct-gap bulk materials

The conditions under which the band gaps of free standing and embedded semiconductor quantum dots are direct or indirect are discussed. Semiconductor quantum dots are classified into three categories; (i) free standing dots, (ii) dots embedded in a direct gap matrix, and (iii) dots embedded in an indirect gap matrix. For each category, qualitative predictions are first discussed, followed by the results of both recent experiments and state of the art pseudopotential calculations. We show that:

A simple model for determining effects of negative differential mobility and magnitude of saturated velocity on the performance of Schottky-barrier field effect transistors

The effects of nonuniform fields in the channel of GaAs MESFETs, and the resulting range of velocities with which carriers drift, are here considered using a simple model in order to determine the effects of negative differential mobility and saturated velocity on the performance of these devices, and of devices made of other materials. On the basis of the equilibrated velocity-field ν(E) characteristic for GaAs, carriers in short-channel FETs drift over much of the source to drain length with the saturated high field velocity, i.e. a velocity about half that used in most previous analytical solutions for GaAs FETs, and one about equal to the maximum carrier velocity in Si. Neglecting transient effects in electron transport, fields at which a negative differential mobility occurs exist over only a very small portion of the channel. The value of low field mobility of the MESFET material is therefore important primarily in determining source resistance.     

The lock-on effect in electron-beam-controlled gallium arsenideswitches

The authors analyze the lock-on effect, which is the inability of photoconductive or electron-beam-controlled semiconductor switches to recover to their initial hold-off voltages following the application of the laser or electron-beam pulse, if the applied voltage exceeds a certain value. For GaAs this threshold voltage corresponds to average electric fields in the range from 4 to 12 kV/cm. Experimental results on semi-insulating GaAs switches indicate that the corresponding lock-on current after e-beam irradiation is identical with the steady-state dark current. The highly resistive state of the switch before e-beam irradiation is shown to be a transient phase towards the much lower steady-state dark resistance, with a duration which depends on the impurity content of the switch material and the applied voltage. The irradiation of the GaAs samples with electrons or photons causes an acceleration of this temporal evolution; at sufficiently high laser or e-beam intensities, lock-on of the dark current after termination of the driving ionization source is observed. Based on the experimental results, a model is developed which describes the lock-on effect in terms of double injection and carrier trapping in deep intraband levels. The model explains the major characteristics of the lock-up effects and is supported by the qualitative agreement of the calculated current-voltage curves with the experimental data     

Impact ionization and light emission in AlGaAs/GaAs HEMT's

Impact ionization and light emission phenomena have been studied in AlGaAs/GaAs HEMTs biased at high drain voltages by measuring the gate excess current due to holes generated by impact ionization and by analyzing the energy distribution of the light emitted from devices in the 1.1-3.1 eV energy range. The emitted spectra in this energy range can be divided into three energy regions: (i) around 1.4 eV light emission is dominated by band-to-band recombination between cold electrons and holes in GaAs; (ii) in the energy range from 1.5 to 2.6 eV energy distribution of the emitted photons is approximately Maxwellian; and (iii) beyond 2.6 eV the spectra are markedly distorted due to light absorption in the n⁺ GaAs cap layer. The integrated intensity of photons with energies larger than 1.7 eV is proportional to the product of the drain and gate currents. This suggests recombination of channel electrons with holes generated by impact ionization as the dominant emission mechanism of visible light     

Electron transport and ionization in silicon at high fields

The saturated drift velocity measured for electrons at high fields is inconsistent with Shockley's model for impact ionization in silicon. It is explained in terms of a field-dependent mean free path for high energy phonon creation in the electric field direction, electrons creating a high energy phonon as soon as they have acquired sufficient energy from the field. Assuming that the electron wavepacket travels at the saturated drift velocity without dispersion, it can be shown that the increased scattering rate at high fields must result in a large spread in the carrier energy. If a drifted Maxwellian distribution is assumed, a unique expression can be obtained for the carrier temperature T^* which is in good agreement with the measured field dependence of the ionization coefficient. In this model, a cylindrical hot carrier distribution must be assumed with the hot carrier energy in a plane perpendicular to the applied field. Exact calculations of the magneto-resistance of such a distribution can be made verifying that the drift velocity is indeed saturated.     

Impact ionization and light emission in InAlAs/InGaAsheterostructure field-effect transistors

We present measurements on impact ionization effects, real space transfer of holes and electrons, and light emission occurring in n-channel InAlAs/InGaGs heterostructure Field-Effect Transistors based on InP operated at high electric fields and at different temperatures. The channel electrons heated by the lateral electric field give rise to impact ionization and light emission. By comparing the electrical characteristics and the integrated light intensity in different energy ranges and at different temperatures, we were able to identify two main different light emission mechanisms: conduction to conduction-band transitions for low energy photons and conduction to valence-band transitions for high energy photons. The correlation between the gate current and the light intensity allowed us to separately evaluate the electron and hole components of the gate current     

InAs/InGaSb photodetectors grown on GaAs bonded substrates

The results of wafer fusion between GaAs and InP followed by transfer of an InGaAs film from the InP to GaAs substrate are presented in this paper. This technique of film transfer allowed the subsequent growth of epitaxial materials with approximately 7% lattice mismatch. Type-II InAs/GaInSb superlattices photodetectors of different designs have been grown by molecular beam epitaxy (MBE) on the alternative InGaAs/GaAs substrate and on standard GaSb substrates. Comparison between photodetectors grown on the two different substrates with nearly identical superlattice periods showed a shift in the cut-off wavelength. The superlattices grown on the alternative substrates were found to have uniform layers, with broader x-ray linewidths than superlattices grown on GaSb substrates.     

High-field transport in organometallic VPE AlxGa1-xAs transferred-electron devices

The velocity-field characteristics of hot electrons in planar organometallic vapor phase epitaxial (VPE) AlxGa1-xAs (0.1 ≤ x ≤ 0.6) transferred-electron devices have been measured by the probe technique. The characteristics in layers with x ≤ 0.30 show normal subthreshold behavior. For x > 0.30, the characteristics exhibit high values of drift velocity. The effects are more enhanced when an undoped 0.4-µm GaAs buffer layer is grown first on the GaAs: Cr substrate before the ternary layer is grown. Monotonically increasing drift velocities with electric field, with a value of 2 × 10⁷cm/s at 6 kV/cm, have been measured in these devices. These effects and overshoots in the pulsed current-time profiles indicate the onset of real-space electron transfer at the heterointerface at high fields.     

Electron properties in GaAs for the design of MM-wave IMPATTs

A very staightforward method has been developed to apply space-charge resistance measurements for determining the high-field drift velocity of electrons in GaAs. The breakdown voltages of the single-drift flat-profile IMPATT diodes used in these measurements justify the validity of well known ionization rates for still higher electric fields.