Trapping and recombination processes via deep level T3 in semi-insulating gallium arsenide

Trapping and recombination of free carriers by deep level T₃ has been studied. Occupancy of the level by electrons and dynamics of its filling and emptying as a function of illumination with monoenergetic photons in 0.69–1.55 eV range has been monitored by the thermally stimulated currents method. We have found that level T₃ behaves more like a recombination center than like an ordinary electron trap. Besides trapping free electrons from conduction band, this trap can also communicate with valence band, trapping holes. The capture cross section for trapping a hole is estimated to be comparable or even larger than the capture cross section for trapping an electron. However, in many experimental conditions free electrons are generated more abundantly than free holes, and free carrier mobility and thermal velocity are both much higher for electrons than for holes. Therefore, electron trapping often prevails, so that this frequently detected defect, has been up to now most often perceived as a deep electron trap.     

Morphological development during platinum/gallium arsenide interfacial reactions

The diffusion path and reaction kinetics of Pt/GaAs diffusion couples were investigated in the temperature range 400 to 1000° C using optical metallography, electron probe microanalysis (EPMA), and scanning electron microscopy (SEM). In all cases the formation of two phases, Pt₃Ga and PtAs₂, was observed. A layered structure Pt/Pt₃Ga/ PtAs₂/GaAs was observed in the temperature range 400 to 450° C and again between 700 and 800° C. However, in the intermediate temperature range from 450 to 650° C a two-phase mixture was observed with the sequence Pt/Pt₃Ga/(Pt₃Ga, PtAs₂)/GaAs. This two-phase microstructure resulted in faster reaction rates than would have been predicted from the layered kinetics. The reversion from the agglomerate two-phase to a layered microstructure between 650 and 675° C may be explained by a rapid rate of grain coarsening in the two-phase microstructure at high temperature. This return to a planar morphology resulted in a substantial decrease in reaction rate with increasing temperature.     

A eutectic dislocation etch for gallium arsenide

A eutectic etchant consisting of 50 mole percent KOH and 50 mole percent NaOH has been developed having a melting point of 170°C. The etchant has an etch rate on 〈100〉 GaAs of 0.2 μm per min at 325°C and is useful on 〈111〉 and 〈100〉 surfaces. The etchant reveals structures not developed with the molten KOH etchant.     

Role of contacts in characterization of deep traps in semi-insulating GaAs by thermally stimulated current spectroscopy

The role of contacts in characterization of traps in semi-insulating (SI) GaAs by thermally stimulated current (TSC) methods has been demonstrated by comparing alloyed In and soldered In contacts. Alloyed In contacts, which have an ohmic characteristic, assure high sensitivities in both TSC and temperature dependent photocurrent (PC), and both are important for determining the trap concentrations in SI GaAs. On the other hand, soldered In contacts, which act like Schottky barriers, cause a significant reduction of both PC and TSC, particularly at low temperatures, and can lead to a misinterpretation of TSC results.     

Surface contamination and damage from CF4 and SF6 reactive ion etching of silicon oxide on gallium arsenide

Two reactive ion etchants, CF₄ and SF₆, have been compared in terms of plasma characteristics, silicon oxide etch characteristics, extent of RIE damage, and formation of barrier layers on a GaAs surface after oxide etch. It was found that higher etch rates with lower plasma-induced dc bias can be achieved with SF₆ plasma relative to CF₄ plasma and that this correlates with higher atomic fluorine concentration in SF₆ plasma. RIE damage, measured by loss of sheet conductance in a thin highly-doped GaAs layer, could be modelled as a region of deep acceptors at a high concentration in the conductive layer. By relating the sheet conductance change to the modelled damaged layer thickness, it was found that the RIE-damaged thickness from both CF₄ and SF₆ plasmas had the same linear relation to plasma dc bias. Barriers to subsequent GaAs RIE were created during oxide overetch at the GaAs surface. The barriers were identified by XPS as ∼20 A of GaF₃ for CF₄ plasma and ∼30 A of GaF₃ on top of As_xS_y for SF₆ plasma. Ellipsometry was used to routinely determine the presence or absence of the barriers which could be removed in dilute ammonia.     

Dielectric constant of semi-insulating gallium arsenide

Results are given on precision measurements of the relative dielectric constant of high-purity semi-insulating gallium arsenide. Using this and other data, it is concluded that the value is within about 0.5% of 12.9, and does not vary significantly between zero frequency and at least 70 GHz.     

Deep traps in GaAs revealed at high resolution by simple fast photocapacitance methods

The characteristics of a new type of capacitance spectroscopy of deep traps in semiconductors are reviewed. A double radiation source technique is employed, the first source controlling the occupation of the traps and the characteristic time constant of the experiment, the second probing the spectral distribution of traps by selectively photoinducing emission to the conduction and valence bands. Time differentiation enhances the detectivity of the traps and minimizes drift problems. Typical spectra obtained with this quasi-equilibrium spectroscopic technique are described. The chromium trap in GaAs presents a distinctive feature with interesting properties which are discussed. Comparisons with thermal capacitance measurements are made, showing the complementary nature of the two methods. The use of the technique to detect out-diffusion of Cr from an insulating substrate into an epitaxial layer is described.     

Correlations of photoluminescence with defect densities in semi-insulating gallium arsenide

Room-temperature luminescence response to a Kr-Ar laser has been used to obtain two-dimensional dislocation maps of LEC GaAs wafers by rastering the laser beam across a wafer surface and storing the response in a computer for subsequent display. One-dimensional line scans of photoluminescence can also be made and indicate a high degree of correlation with the dislocation density. Epitaxial layers, however, show almost no correlation between PL and dislocations and are much "brighter" than bulk-grown material, while Cr-doped HB wafers show only a slight correlation and are much "dimmer" than LEC material. A degradation of luminescence with time is observed when the laser beam is maintained on a single spot, and this decrease is faster as the incident power is increased. Surface recombination, nonradiative recombination, and refractive index variations have been investigated to explain the PL behavior and the result is that non-radiative recombination (or radiative recombination at energies less than I.1 eV) is dominant, and that the effect of dislocations in LEC material is to getter nonradiative recombination centers.     

Minority carrier traps in epitaxial gallium arsenide phosphide

The optical injection of minority carriers in the depletion region of a reverse biased Schottky barrier has permitted the study of deep levels in vapour phase epitaxial n-type GaAsP (Te) structures. The deep level transient spectroscopy (DLTS) experiments have yielded two hole traps at (E_v + 0.60)eV and (E_v + O.36)eV. Additional subsidiary transient capacitance, photocurrent and capture experiments are analysed, the details of which give electron and hole capture cross-sections, trap densities and activation energies. Derived values of minority carrier lifetime (~1 ns) agree with experimental values and with injection-level dependent LED efficiency.     

Characteristics of nuclear radiation detectors based on semi-insulating gallium arsenide

The characteristics of detectors based on bulk semi-insulating GaAs (SI-GaAs) have been studied by α particle detection and spectrometry. A distinctive feature of these detectors is the dependence of the width of the space charge region W on reverse bias voltage U. The rate of increase in W(U) is ∼1 μm/V, which permits formation of a sensitive region a few millimeters thick. The main obstacle to applying kilovolt-range bias voltages U is the reverse current noise. The characteristics of diode structures in which a rectifying barrier to SI-GaAs was formed by metal deposition (Schottky diodes) and by growing heterostructures with heavily doped AlGaAs or GaAsSb epitaxial layers were compared. Nonequilibrium carrier transport in epitaxial structures capable of sustaining bias voltages above 1 kV was investigated in both weak (below 1 kV/cm) and strong (10–30 kV/cm) electric fields. In both cases, the carrier lifetimes were found to be about a few nanoseconds. Such low values are due to the high concentration of trapping centers (EL2-type native defects), which limits the carrier transport. An analysis of the spectral line shape revealed that the lifetime is almost constant throughout the detector volume. The charge introduced by a particle was found to be enhanced in fields of ∼30 kV/cm. This effect can be qualitatively explained by focusing the electric field lines at the vertex of the α-particle track, which leads to an increase in the local field strength to ∼10⁻⁵ V/cm and impact ionization by nonequilibrium electrons. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 4, 2004, pp. 490–497. Original Russian Text Copyright ? 2004 by Verbitskaya, Eremin, Ivanov, Strokan, Vasil'ev, Gavrin, Veretenkin, Kozlova, Kulikov, Markov, Polyakov.     

Effects of melt composition on deep electronic states and compensation ratios inn-type LEC gallium arsenide

In this paper it is shown that the melt composition is a key parameter in the crystal growth of GaAs as it strongly affects the concentration of deep electron levels as well as the electrical activity of the silicon atoms added to the melt in order to get an-type material. Experimental data collected on several samples are included. The correlations between melt stoichiometry and generation/annihilation of point defects as well as electronic properties are discussed considering the existing literature references.     

Photopiezoelectric induction of resonant acoustic waves in semi-insulating gallium arsenide single crystals

The effect of resonant acoustic wave excitation in semi-insulating gallium-arsenide single crystals is investigated by means of light pulses. The peak amplitude of excited elastic oscillations is observed in a temperature range, where small values of the internal friction and electrical conductivity of the semiconductor take place simultaneously. The effect is related to the inverse piezoelectric conversion of the bulk-photovoltage energy into the mechanical deformation of the semiconductor crystal. The results of the investigations can be used for designing semiconductor photodetectors with high modulation-frequency selectivity.     

Numerical simulation of the response of substrate traps to a voltage applied to the gate of a gallium arsenide field effect transistor

We report on a numerical simulation of the response of substrate traps to a voltage applied to the gate of a gallium arsenide field effect transistor (GaAs FET) using proprietary simulation software. The substrate is assumed to contain shallow acceptors compensated by deep levels. The ratio between the densities of deep and shallow levels is considered to be one hundred, which is a typical value for semi-insulating substrates. Although several traps may be present in the substrate but only the most commonly observed ones are considered, namely hole traps related to Cu and Cr, and the familiar native electron trap EL2. The current–voltage characteristics of the GaAs FET are calculated in the absence as well as in the presence of the above mentioned traps. It was found that the hole traps are affected by the gate voltage while the electron trap is not. This effect on the response of hole traps is explained by the fact that the quasi-hole Fermi level in the substrate is dependent on the gate voltage. However, the electron quasi-Fermi level in the substrate is insensitive to the gate voltage and therefore electron traps are not perturbed.     

Gallium arsenide and (alga)as devices prepared by Liquid-Phase epitaxy (Review Article)

Gallium arsenide and (AlGa)As devices and their preparative techniques based on liquid-phase epitaxy are reviewed. Included are discussions of dopants, growth apparatus and structures used in light emission, electron emission, photodetection, and microwave systems.     

Electron traps in thin layers of low-temperature-grown gallium arsenide with As-Sb nanoclusters

Electron traps in low-temperature-grown ～40-nm-thick GaAs layers containing nanometer As-Sb clusters have been studied using deep-level transient spectroscopy. Measurements at various bias voltages and small-amplitude filling pulses have allowed the identification of two groups (T1 and T2) of traps with substantially different thermal electron emission rates. It is shown that the density of traps T2 (with an activation energy of 0.56 ± 0.04 eV and electron capture cross section of 2 × 10^?13?10^?12cm²) is ～2 × 10¹²cm_?2, while the density of traps T1 (0.44 ± 0.02 eV and 2 × 10^?14?10^?13 cm², respectively) is ten times lower. It is assumed that, according to the existence of the two cluster groups observed in the layers under study, traps T2 are associated with clusters 4–7 nm in diameter and traps T1, with clusters up to ～20 nm in diameter.     

A first-principles study of transport properties of a gallium arsenide nanoribbon-based molecular device

GaAs nanoribbon based molecular device is investigated using density functional theory. The electronic transport properties of GaAs nanoribbon are discussed in terms of density of states, electron density, transmission spectrum and transmission pathways. The applied bias voltage increases the peak maximum in the valence band and the conduction band. The electron density is found to be more on the arsenic sites than in gallium sites across GaAs nanoribbon. The transmission spectrum provides the insight to the transmission of electrons at different energy intervals across GaAs nanoribbon. The transmission pathways give the visualization of possible path for the electrons, when the bias voltage is varied between the electrodes. The transmission pathways get modified with the applied bias voltage. The result of the present study gives clearer vision of enhancing the electronic transport properties of GaAs nanoribbon which is used in optoelectronic devices.