Single-crystal GaAs Wafers Research Articles

Резонансная микроволновая спектроскопия полупроводников с микронным разрешением

We have proposed and experimentally verified a local method of microwave resonant spectroscopy of semiconductors. The microwave circuit of the spectrometer based on the Cascade Microtech probe station is equipped with a coaxial resonator of special geometry. As result, the measurement accuracy of the previously developed volt-impedance spectroscopy method was greatly increased. A technique for spectrometer calibration and resonant measurements of the complex impedance of the probe-sample system has been developed. We have measured the impedance of test structures with Schottky contacts of 30 - 60 μm in diameter on a single-crystal GaAs wafer at several discrete frequencies in the range of 50 - 250 MHz. The nontrivial resistive properties of the structures are studied, which consist of the excess resistance that is 1–2 orders higher than the spreading resistance for the alternating current in the unperturbed region of the semiconductor. The discovered effect is presumably associated with the a.c. charge modulation on deep levels of the semiconductor. A model calculation of the impedance spectrum has been performed, which demonstrates a good agreement with the experimental spectra.

Microwave Resonant Spectroscopy of Semiconductors with Micrometer Resolution

We have proposed and experimentally verified a local method of microwave resonant spectroscopy of semiconductors. The microwave circuit of the spectrometer based on the Cascade Microtech probe station is equipped with a coaxial resonator of special geometry. As result, the measurement accuracy of the previously developed volt-impedance spectroscopy method was greatly increased. A technique for spectrometer calibration and resonant measurements of the complex impedance of the probe-sample system has been developed. We have measured the impedance of test structures with Schottky contacts of 30-60 μm in diameter on a single-crystal GaAs wafer at several discrete frequencies in the range of 50-250 MHz. The nontrivial resistive properties of the structures are studied, which consist of the excess resistance that is 1-2 orders higher than the spreading resistance for the alternating current in the unperturbed region of the semiconductor. The discovered effect is presumably associated with the a.c. charge modulation on deep levels of the semiconductor. A model calculation of the impedance spectrum has been performed, which demonstrates a good agreement with the experimental spectra. Keywords: Microwave microscope, near field, probe, resonator, impedance, semiconductor.

Microwave Resonant Spectroscopy of Semiconductors with MicrometerResolution

We have proposed and experimentally verified a local method ofmicrowave resonant spectroscopy of semiconductors. The microwave circuit ofthe spectrometer based on the Cascade Microtech probe station is equippedwith a coaxial resonator of special geometry. As result, the measurementaccuracy of the previously developed volt-impedance spectroscopy method wasgreatly increased. A technique for spectrometer calibration and resonantmeasurements of the complex impedance of the probe-sample system has beendeveloped. We have measured the impedance of test structures with Schottkycontacts of 30-60 μm in diameter on a single-crystal GaAs wafer at severaldiscrete frequencies in the range of 50-250 MHz . The nontrivial resistiveproperties of the structures are studied, which consist of the excessresistance that is 1-2 orders higher than the spreading resistance for thealternating current in the unperturbed region of the semiconductor. Thediscovered effect is presumably associated with the a.c. charge modulationon deep levels of the semiconductor. A model calculation of the impedancespectrum has been performed, which demonstrates a good agreement with theexperimental spectra. Keywords: Microwave microscope, near field, probe, resonator, impedance, semiconductor.\

Microwave Volt–Impedance Spectroscopy of Semiconductors

The previously proposed technique of microwave volt–impedance spectroscopy of semiconductors has been experimentally verified. The technique allows one to determine the local values of electrical parameters of a semiconductor. The investigations have been carried out on a homogeneous single-crystal GaAs wafer with a system of concentric antennas formed on the top of it. The resolution is determined by the antenna central disk diameter, which has been 12, 27, and 57 μm. A dc bias voltage of 0 V ≤ U ≤ 5 V has been applied between antenna contact pads. The complex Z(f, U) impedance spectrum of each antenna has been measured on a Cascade Microtech probe station in the frequency range of f = 0.1–10 GHz. The electrical characteristics of the semiconductor have been determined from the Z(f, U) spectra by solving the inverse problem. The n-type of the semiconductor has been established, and the contact potential difference at the interface with a metal has been determined. The local values of electron density, mobility and electrical conductivity have been found have been found. The four-point probe Hall effect measurements of the surface-averaged values of the same parameters have shown good agreement of the results for the investigated homogeneous wafer.

Микроволновая вольт-импедансная спектроскопия полупроводников

We have tested experimentally the proposed method of microwave volt-impedance spectroscopy of semiconductors. The method allows to determine the local values of the semiconductor electrophysical parameters. The studies were performed on a homogeneous single-crystal GaAs wafer with a concentric antenna system formed on its surface. The resolution is determined by the diameter of the antenna central disk, which was amounted a = 12, 27, 57 μm. A constant bias voltage of 0 ≤ U ≤ 5 V was applied between the contact pads of the antennas. The complex impedance spectrum Z (f, U) of each antenna was measured using a Cascade Microtech probe station in the frequency range f = 0.1 - 10 GHz. The electrophysical characteristics of the semiconductor were determined from Z(f, U) spectra by the inverse problem solving. We have established the n-type for our semiconductor and determined the electrical potential difference on the metal-semiconductor interface. We have found as well the electron concentration, mobility and conductivity. Measurements of the same parameters by Hall four-probe method (giving the surface averaging) showed good mutual agreement of the results for the homogeneous sample under study.

Preparation of Dielectric Films via Thermal Oxidation of MnO2/GaAs

MnO2 nanolayers (~29 nm) produced on the surface of single-crystal GaAs wafers by magnetron sputtering have been shown to act as oxygen transfer agents for the thermal oxidation of the semiconductor. The presence of MnO2 increases the oxide film growth rate by three to nine times relative to stimulator-free oxidation of GaAs. The films thus grown range in thickness from 35 to 200 nm and possess good dielectric properties (resistivity on the order of ~1010 Ω cm and dielectric strength in the range (5–8) × 106 V/cm). According to X-ray diffraction data, the films are enriched in oxidized arsenic and have a regular grain structure in the surface layer, with a roughness height within 30 nm (according to atomic force microscopy data).

Investigation on damage process of GaAs induced by 1064nm continuous laser

A single crystal GaAs wafer with front face mirror polished was irradiated by a 1064nm continuous laser experimentally. The damage process was investigated by real-time surface reflectivity and optical distribution monitoring. No evident melting and oxidation occurrence was found and the components of Ga and As almost kept constant during the whole damaging process. The distinct differences from the damage by 532nm continuous laser were analyzed as well. For the current wavelength, the damage threshold was greatly dependent on the boundary conditions, consequently only an estimated threshold value about 2kW∕cm2 was obtained.

Effects of optical absorption onGa71optically polarized NMR in semi-insulating GaAs: Measurements and simulations

The intensity and the hyperfine shift of optically polarized NMR (OPNMR) signals of $^{71}\mathrm{Ga}$ in semi-insulating GaAs have been found to depend on the photon energy and the helicity of light used for optical pumping. Single-crystal GaAs wafers of two different thicknesses, 400 and $175\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$, were examined. The maximum intensity of the OPNMR signals was observed well below the band gap energy, and this maximum OPNMR signal shifted to higher photon energies for the thinner sample. In the range of photon energies for which the maximum OPNMR signals are obtained, there is little or no hyperfine shift of the $^{71}\mathrm{Ga}$ OPNMR resonance. Hyperfine shifts with the largest magnitude are recorded for photon energies at or above the band gap. At a given photon energy, asymmetric OPNMR signals were observed, with ${\ensuremath{\sigma}}^{+}$ light producing a more intense emissive signal than the corresponding absorptive signal coming from ${\ensuremath{\sigma}}^{\ensuremath{-}}$ light. We developed a model that accounts for optical absorptivity of GaAs in order to simulate the observed OPNMR intensity, the change in the OPNMR maximum for the thinner sample, and the hyperfine shift dependence on photon energy. This model also accounts for the asymmetric OPNMR intensity for the two ${\ensuremath{\sigma}}^{+}$ and ${\ensuremath{\sigma}}^{\ensuremath{-}}$ helicities of light. The intensity dependence of the OPNMR signals arises as a consequence of two competing factors: the optical absorptivity of GaAs which directly impacts nuclear polarization $⟨{I}_{Z}⟩$, and the number of accessible nuclear spins. The magnitude of the hyperfine shift of the OPNMR signals reflects the probability of occupation of optically relevant defects in the semiconductor, also related to optical absorptivity. Finally, the asymmetry in the OPNMR signals arises from the sign of electron spin polarization produced in the optical pumping process.

Effect of irradiation with low-energy Ar ions on the characteristics of the working and rear sides of single-crystal GaAs substrate

Contactless methods were used to study the characteristics of the front and rear sides of single-crystal GaAs wafers whose rear side was irradiated with low-energy Ar ions. Variations in the optical and photoelectric properties of irradiated and unirradiated sides were detected. A solitonic mechanism for the penetration of defects into the crystal bulk is suggested.

Q switching of a diode-pumped Nd:YAG laser with GaAs

We investigated the properties of a diode-pumped Nd:YAG laser that is passively Q switched by a thin, singlecrystal GaAs wafer. At 3 W of incident pump power, the laser produced stable 7-ns pulses with 20 microJ of energy at a 6-kHz repetition rate. For pump powers up to 2.2 W, which resulted in 13.2-microJ pulses, the output mode was TEM(00). The shortest pulses that we observed were 3 ns in duration. In addition to saturable absorption, we find that two-photon absorption and free-carrier effects determine pulse formation.

Direct adhesion of single-crystal GaAs wafers

Bonding of two single-crystal GaAs wafers is reported. The bonding process includes a heat treatment at 850°C in flowing hydrogen ambient. High-resolution transmission microscopy observation shows that the two wafers are bonded directly. Disorder in lattice pattern was also observed instead of clear bonding seam. A simple argument on adhesion mechanism is also given.