Gallium Arsenide Epitaxial Layers Research Articles

Investigation of fused ohmic contacts to epitaxial layers of gallium arsenide alloyed by tellurium

Investigation of fused ohmic contacts to epitaxial layers of gallium arsenide alloyed by tellurium

Studying the Effect of Electrically Active Impurities Coming from Trimethylgallium Synthesized by Different Means on the Electrophysical Characteristics of Gallium Arsenide Epitaxial Layers

Chemical deposition from vapors of metalorganic compounds and volatile hydrides (metalorganic vapor phase epitaxy) is the main way of growing devices’ heteroepitaxial structures based on gallium arsenide (GaAs) and solid solutions of it (AlxGa1 – xAs and InyGa1 – yAs) on an industrial scale. Electrically active impurities deposited uncontrollably on epitaxial layers during growth worsen the electrophysical parameters of devices’ structures. Sources of deposited background impurities include the initial material. In this work, ways of synthesizing trimethylgallium (TMG) are compared from the viewpoint of impurities, especially electrically active GaAs, being incorporated into the final product. Ways of preparing TMG that include the exchange reaction between gallium trichloride and trimethylaluminum (TMA) and magnesium–organic syntheses in which metallic magnesium is used as the initial reagent are selected as the objects of study. The behavior of electrically active impurities during the purification of TMG via rectification is studied. The investigations are performed by means of spectral analysis and functional control over the growth of electrophysical parameters of GaAs epitaxial layers from TMG and arsine. It is established that the qualitative and quantitative composition of impurities in TMG depends on their content in the initial reagents. TMG prepared using the exchange reaction between gallium trichloride and TMA is the source of n-type impurities in GaAs. These are mainly Group IV elements (silicon, tin, and lead), with silicon impurities predominating. TMG fabricated using metallic magnesium is a source of both p- (preferentially zinc) and n-type (preferentially silicon) impurities. Irrespective of the quality of the initial raw TMG, the use of reduced-pressure rectification allows the fabrication of TMG with low impurity contents. Epitaxial GaAs layers grown using purified TMG (TMG rectificate) have n-type conduction with a low level of background doping (0.7–4) × 1014 cm–3 and high carrier mobilities of 7300–8500 cm2/(V s) at 300 K and 90 000–156 000 cm2/(V s) at 77 K. These values correspond to purest samples made with TMG and arsine using MOC-hydride epitaxy. Based on the data on functional control, the content of impurities that display electrical activity in GaAs is on the level of 10−7–10−6 at % in fabricated TMG-rectificate samples.

Исследование влияния электрически активных примесей, поступающих из синтезированного различными методами триметилгаллия, на электрофизические характеристики эпитаксиальных слоев арсенида галлия

Исследование влияния электрически активных примесей, поступающих из синтезированного различными методами триметилгаллия, на электрофизические характеристики эпитаксиальных слоев арсенида галлия

Precision calibration of the silicon doping level in gallium arsenide epitaxial layers

An approach to precision calibration of the silicon doping level in gallium arsenide epitaxial layers is discussed that is based on studying the dependence of the carrier density in the test GaAs layer on the silicon- source temperature using the Hall-effect and CV profiling techniques. The parameters are measured by standard or certified measuring techniques and approved measuring instruments. It is demonstrated that the use of CV profiling for controlling the carrier density in the test GaAs layer at the thorough optimization of the measuring procedure ensures the highest accuracy and reliability of doping level calibration in the epitaxial layers with a relative error of no larger than 2.5%.

Research into constructive and technological features of epitaxial gallium-arsenide structures formation on silicon substrates

The technology of formation of LSI structures on GaAs epitaxial layers, formed on Si-substrates of large diameter, is developed, which makes it possible at least by an order of magnitude to reduce the production cost of crystals due to epitaxial growth of GaAs layers and the use of technological equipment of silicon technology. This technology also enables the useof heterostructures to increase the speed of the LSI. An analysis of complex structures of different architecture of IC/LSI on GaAs epitaxial layers, formed on Si-substrates, is carried out. The influence of the scattering processes of charge carriers on the potential fluctuations on the magnitude and profile of the mobility of electrons along the thickness of the epitaxial structure is investigated. When using epitaxial technology in structures, there are no isoconcentric impurities of oxygen and carbon, which are the factors of scattering of charge carriers, which makes it possible to achieve high values of mobility of charge carriers. It is shown that the use of epitaxial layers of gallium arsenide eliminates the effects of isoconcentration impurities of oxygen and carbon in gallium arsenide layers that increases their purity. A test element was implemented that allows non-destructive measurement of the mobility of charge carriers in the technological cycle of the formation of LSI structures. This allows us to realise the electrophysical diagnosis of the reliability of the LSI at the stage of crystal manufacturing

Photoelectric characteristics of metal-Ga2O3-GaAs structures

We investigate the effect of thermal annealing in argon and of oxygen plasma processing on the photoelectric properties of GaAs-Ga2O3-Me structures. Gallium-oxide films are fabricated by photostimulated electrochemical oxidation of epitaxial gallium-arsenide layers with n-type conductivity. The as-deposited films were amorphous, but their processing in oxygen plasma led to the nucleation of β-Ga2O3 crystallites. The unannealed films are nontransparent in the visible and ultraviolet (UV) ranges and there is no photocurrent in structures based on them. After annealing at 900°C for 30 min, the gallium-oxide films contain only β-Ga2O3 crystallites and become transparent. Under illumination of the Ga2O3-GaAs structures with visible light, the photocurrent appears. This effect can be attributed to radiation absorption in GaAs. The photocurrent and its voltage dependence are determined by the time of exposure to the oxygen plasma. In the UV range, the sensitivity of the structures increases with decreasing radiation wavelength, starting at λ ≤ 230 nm. This is due to absorption in the Ga2O3 film. Reduction in the structure sensitivity with an increase in the time of exposure to oxygen plasma can be caused by the incorporation of defects both at the Ga2O3-GaAs interface and in the Ga2O3 film.

Closed cycle chiller as a low cost alternative to liquid nitrogen in molecular beam epitaxy

The high cost of cooling the cryoshroud in a molecular beam epitaxy system has been greatly reduced by replacing liquid nitrogen (LN2) as a coolant with a silicone polymer heat transfer fluid cooled to as low as −80 °C by a closed cycle chiller. Gallium arsenide epitaxial layers have been grown with two different cooling configurations of the shroud: conventional LN2 cooling and cooling to −70 °C with the chiller. The partial pressure of water in the chamber is a factor of about 2.5 higher with the closed cycle chiller operating at −70 °C than with liquid nitrogen in the shroud. No significant difference is observed in the density of deep levels in the GaAs, as determined by deep level transient spectroscopy.

Spin Relaxation in GaAs Doped with Magnetic (Mn) Atoms

The GaAs doped with donors manifests long times of spin relaxation, while in the case of acceptors (or magnetic impurities) spin relaxation rate increases markedly, in accordance with theoretical predictions. From the practical point of view, this situation is unfavorable, since the devices based on spin degrees of freedom require long times of the spin memory. Therefore semiconductors such as p-GaAs were not considered as promising materials for spintronics. In the present work this conclusion is refuted by means of investigation of the spin dynamics of electrons in epitaxial layers of gallium arsenide doped with Mn impurities. In spite of the expectations, we have discovered the suppression of the spin relaxation of electrons in GaAs:Mn by two orders of magnitude. This effect is a consequence of compensation of the hole and manganese effective magnetic fields due to the antiferromagnetic interaction. The analogous results obtained for the case of GaAs quantum well doped with Mn [R. C. Myers, et al., Nature Materials 7, 203 (2008)] were interpreted as the result of the spin precession of magnetic acceptors rather than electrons. Through separate measurements of g-factor by means of time resolved spectroscopy it has been proved that long times of spin relaxation in p-GaAs:Mn relate to electrons and not to magnetic acceptors. The oscillation frequency of the angle of Kerr rotation depends linearly on the magnetic field and complies with g=0.46±0.02, i.e. the electronic g-factor.

Use of epitaxial gallium arsenide in detectors

The results of investigations of semiconductor detectors on the basis of epitaxial layers of gallium arsenide for detecting x rays and low-energy radiation are examined. It is shown that epitaxial layers ranging in thickness from 60 to 300 µm with current carrier density ≤5·1013 cm−3 and electron mobility ≥6000 cm2/(V·sec) at 300 K hold promise for such detectors.

Coherent spin manipulation without magnetic fields in strained semiconductors

A consequence of relativity is that in the presence of an electric field, the spin and momentum states of an electron can be coupled; this is known as spin-orbit coupling. Such an interaction opens a pathway to the manipulation of electron spins within non-magnetic semiconductors, in the absence of applied magnetic fields. This interaction has implications for spin-based quantum information processing and spintronics, forming the basis of various device proposals. For example, the concept of spin field-effect transistors is based on spin precession due to the spin-orbit coupling. Most studies, however, focus on non-spin-selective electrical measurements in quantum structures. Here we report the direct measurement of coherent electron spin precession in zero magnetic field as the electrons drift in response to an applied electric field. We use ultrafast optical techniques to spatiotemporally resolve spin dynamics in strained gallium arsenide and indium gallium arsenide epitaxial layers. Unexpectedly, we observe spin splitting in these simple structures arising from strain in the semiconductor films. The observed effect provides a flexible approach for enabling electrical control over electron spins using strain engineering. Moreover, we exploit this strain-induced field to electrically drive spin resonance with Rabi frequencies of up to approximately 30 MHz.

Picosecond high-voltage drift diodes based on gallium arsenide

Experimental results of studying the dynamics of recovery of diodes based on lightly doped epitaxial layers of gallium arsenide are reported. The diodes under consideration belong to the class of drift diodes with step recovery and are designed to operate in circuits for shaping and generating picosecond pulses. The obtained values of the reverse-voltage recovery rate (dU/dt≈2000 V/ns) far exceed the published ultimate recovery rates for picosecond-response diodes with charge accumulation and are unprecedentedly high for step-recovery drift diodes.

Features of the photoluminescence of epitaxial layers of GaAs grown from the vapor phase on silicon substrates

This paper presents the results of studies of the photoluminescence intensity distribution in various sections of the surface of epitaxial layers of gallium arsenide grown on silicon substrates. It is established that the epitaxial layers have a block structure in the form of radiative areas separated by dark (nonradiative) boundaries, whose shape depends on the substrate's crystallographic orientation. It is assumed that the block structure is associated with internal stresses that arise in the epitaxial layers because of differences of the lattice constants and thermal expansion coefficients of the connected materials.

Growth of high purity liquid phase epitaxial GaAs in a silica growth system

Liquid phase epitaxial gallium arsenide layers, greater than 200 μm thickness and with a low net carrier concentration ( N A,D ≈ 10 13 cm −3) have been grown in a silicia growth system with silica crucibles. Analysis of electrical and chemical defects was carried out using capacitance-voltage ( C V) measurements, deep level transient spectroscopy (DLTS) and secondary ion mass spectroscopy (SIMS). Details of the growth procedure are given and it is shown that silicon incorporation in the growth layer is not suppressed by the addition of ppm levels of oxygen to the main hydrogen flow.

Electrophysical properties of epitaxial gallium arsenide doped with acceptor impurities

Epitaxial layers of gallium arsenide doped with zinc and cadmium were grown in a chloride vapor-transport system using diethylzinc and dimethylcadmium as the sources of the impurity. We studied the effect of the inlet pressure of the impurities and the growth temperature on the doping level of the layers. We investigated the temperature dependences of the hole concentration and mobility in layers doped with zinc and cadmium up to different levels.

Nucleation and growth of gallium arsenide on silicon (111)

The nucleation and growth of undoped gallium arsenide (GaAs) epitaxial layers, grown by metalorganic vapour phase epitaxy (MOVPE) on Si (111) substrates were investigated by transmission electron microscopy (TEM). The initial stages of epitaxial growth are considered at high and low growth temperatures. The influence of growth time and thermal annealing on the initial stages of growth are also studied and reported.

Use of low-frequency capacitance in deep level transient spectroscopy measurements to reduce series resistance effects

In this article, we demonstrate the usefulness of a low-frequency capacitance deep level transient spectroscopy (LFDLTS) technique suitable for samples with a large built-in resistance in series with the depletion capacitance. As a case study, we investigate the effects of series resistance arising from the contact resistance and the bulk resistance of aluminum gallium arsenide epitaxial layers grown on semi-insulating gallium arsenide substrates. We show that there can be significant errors in the density and the activation energy of the traps (the so-called DX centers) determined by the conventional high-frequency (1 MHz) capacitance deep level transient spectroscopy measurements when the series resistance associated with the sample is high. On the other hand, the LFDLTS measurements are found to be free from these artifacts related to the series resistance effects.

The characterisation of GaAs on silicon using polarised laser light

AbstractMBE‐grown gallium arsenide epitaxial layers on silicon, with thicknesses between 0.1 and 8.1 μm, have been studied using a simple rotating polariser multiple‐angle‐of‐incidence ellipsometer. From these data, information on the roughness of the surfaces of the layers and the anisotropy of the refractive index of the layers has been obtained. The results are compared with data obtained on the same samples using scanning electron microscopy and conventional spectroscopic ellipsometry.

Structural characterization of gallium arsenide epitaxial layers grown on Si(001)

The nucleation and growth of undoped gallium arsenide (GaAs) epitaxial layers, grown by metallo-organic vapour-phase epitaxy (MOVPE) on Si (001) substrates, were investigated by transmission electron microscopy (TEM). The influence of growth time and thermal annealing on the initial stages of growth was mainly considered. TEM studies indicated that GaAs nucleates in the form of three-dimensional epitaxial islands on Si (001) and eventually coalesced into a continuous film as growth proceeds. Dark-field TEM studies showed that high densities of primary and tertiary twins are present in the epitaxial (001) GaAs buffer layers. These microtwins, present in the epitaxial buffer layers, are able to extend to the top surface of the subsequently grown layers and were found to be the main reason for the degradation in the surface morphology of GaAs-on-Si layers.

The calibration of the strength of the localized vibrational modes of silicon impurities in epitaxial GaAs revealed by infrared absorption and Raman scattering

n-type silicon-doped epitaxial layers of gallium arsenide grown by molecular-beam epitaxy (MBE) or metal-organo chemical vapor deposition (MOCVD) have been investigated by measurements of the Hall effect and the strengths of the localized vibrational modes (LVM) of silicon impurities using both Fourier transform absorption spectroscopy and Raman scattering at an excitation energy of 3 eV close to the E1 band gap. Lines from Si(Ga) donors, Si(As) acceptors, Si(Ga)-Si(As) pairs, and Si-X, a complex of silicon with a native defect, were detected and correlated for the two techniques. The maximum carrier concentration [n] found for samples grown under standard conditions was 5.5×1018 cm−3. At higher doping levels Si-X becomes dominant and acts as an acceptor, so reducing [n]. An integrated absorption of 1 cm−2 in the Si(Ga) LVM line corresponds to 5.0±4×1016 atoms cm−3: a similar calibration applies to the Si(As) line, but for Si-X, an absorption of 1 cm−2 corresponds to only 2.7±1.0×1016 defects cm−3. Possible structures for Si-X are discussed but a definitive model cannot yet be proposed. MBE samples grown at 400 °C had values of [n] close to 1019 cm−3, and a negligible concentration of Si-X. On annealing, [n] decreased and Si-X defects were produced together with site switching of Si(Ga) to Si(As). These results are important to the understanding of the mechanism of silicon diffusion at low temperatures. The infrared absorption and Raman measurements are complementary. Absorption measurements made at a resolution of 0.1 cm−1 require layers greater than or equal to 1 μm in thickness doped to a level of 3×1017 cm−3 but require the prior elimination of free-carrier absorption. Raman measurements can be made on as-grown layers only 10 nm in thickness doped to a level of 2×1018 cm−3, but with a spectral resolution of only 5 cm−1.

An homogeneous growth model of gallium arsenide epitaxial layers from the gas phase

This paper represents a continuation and ending of the kinetic study of the gallium arsenide formation, where a so-called inhomogeneous model is proposed and quantitatively formulated in five variants, in which two kinds of active centres appear. This model is compared both with the experimental data and with the previous sequence of homogeneous models.