Semi-insulating Gallium Arsenide Substrates Research Articles

Carrier mobility dependence of indium antimonide-bismide on carrier concentration, temperature, and bismuth composition grown on semi-insulating gallium arsenide substrate

We explore the impact of carrier concentration, temperature, and bismuth (Bi) composition on the carrier mobility of indium antimonide-bismide (InSb1−x Bi x ) material. Utilizing the molecular beam epitaxy method, we achieved high Bi composition uniformity. This method also enables the InSb1−x Bi x to be grown on semi-insulating GaAs substrate, effectively preventing parallel electrical conduction during Hall effect measurement. Our findings reveal that InSb1−x Bi x doped with silicon (Si) and tellurium (Te) consistently exhibit n-type conductivity. In contrast, InSb1−x Bi x doped with beryllium (Be) exhibit a transition from n to p type conductivity, subjected to the Be doping level and the measurement temperature. Based on these observations, we proposed an empirical model describing the dependence of InSb1−x Bi x electron mobility on carrier concentration, temperature, and Bi composition, specifically for Si and Te-doped InSb1−x Bi x samples. These insights gained from this study hold potential application in photodetector device simulations.

Dopant profiling of ion-implanted GaAs by terahertz time-domain spectroscopy

We investigate terahertz time-domain spectroscopy (THz-TDS) as a non-destructive and non-contact technique for depth profiling of dopants in semiconductors. THz temporal waveforms transmitted through silicon-ion-implanted semi-insulating gallium arsenide substrates, as-implanted or post-annealed by rapid thermal annealing, were analyzed by assuming a multi-layered Gaussian refractive index profile in the ∼sub-micrometer-thick implantation region. The implantation energy and dosages in this work were 200 KeV, 1014, 5 × 1014, and 1015 ions/cm2, respectively. The average values of real (n) and imaginary (κ) parts of refractive indices of an as-implanted sample in the depth range of 0–800 nm are 5.8 and 0.7, respectively, at 0.5 THz and are 6.2 and 0.2, respectively, at 1 THz. On the other hand, the refractive index profile of the post-annealed samples displays a prominent Gaussian-like form, and peak refractive indices (n ∼ 25 and κ ∼ 32.7 at 0.5 THz and n, κ ∼17 at 1 THz) were found to be at the depth of 210 nm. Reconstructed dopant profiles in as-implanted, implanted, and post-annealed substrates were found to be in good agreement with measurements by secondary ion mass spectroscopy as well as simulation by the Monte Carlo method. We were also able to determine accurately the projected range (Rp), straggle (Rs), and concentration of dopants by the analysis of THz-TDS data. The spatial resolution, along the depth direction, of the THz-TDS technique for depth profiling of dopants was estimated to be as small as 8-nm. This work suggests the feasibility of using THz-TDS for nondestructive and non-contact diagnostics for profiling dopants in semiconductors.

Enhanced Optically–Excited THz Wave Emission by GaAs Coated with a Rough ITO Thin Film

In this study, we report enhancement of terahertz (THz) radiation with indium-tin-oxide (ITO) thin-film deposited on semi-insulating gallium arsenide substrate (SI-GaAs). The amplitude of THz emission from both ITO/SI-GaAs and bare SI-GaAs substrate as a function of optical pump (i) incident angle, (ii) polarization angle, and (iii) power were investigated. The enhancement of peak amplitude of a THz pulse transmitted through the ITO/SI-GaAs sample in comparison to bare SI-GaAs substrate varied from 100% to 0% when the pump incidence angle changed from 0° to 50°. The maximum enhancement ratio of peak amplitude for a coated sample relative to the bare substrate is approximately up to 2.5 times at the minimum pump intensity of 3.6 TW/m2 and gradually decreased to one at the maximum pump intensity of 20 TW/m2. From outcomes of these studies, together with data on surface and material characterization of the samples, we show that THz emission originates from the ITO/GaAs interfaces. Further, both interface-field-induced transient current and field-induced optical rectification contribute to the observed THz signal. Observed enhancement was tentatively attributed to surface-plasmon-induced local field enhancement, coupled with constructive interference of forward and retro-reflected backward THz emission from the ITO/GaAs interfaces. The polarity-flip reported previously for very thin Au-coated GaAs was not observed. This was explained by the wide-bandgap, transparency and lower free carriers of ITO. For best results, the incident angle should be in the range of 0 to 30° and the incident polarization should be 0 to 45°. We further predict that the ITO thin film of suitable thickness or with engineered nanostructures, post-annealed under optimum conditions may lead to further enhancement of THz radiation from ITO-coated semiconductor surfaces.

Characteristics of Terahertz Radiation Emitted From Fractal Photoconductive Antennas

We study the terahertz (THz) emission characteristics of a photoconductive antenna comprising a metallic fractal pattern fabricated on a semi-insulating gallium arsenide substrate. multifrequency emission peaks were observed owing to the property of the multifrequency resonances of our fractal structures. The number of emission peaks increases with the number of fractal levels, attributable to the attendant increase in the number of localized resonances. We have also found that the emission intensity of the THz radiation can be enhanced by modifying part of the fractal pattern.

Emission of terahertz radiations from fractal antennas

We investigate the emission of terahertz radiation from a photoconductive fractal antenna fabricated on a semi-insulating gallium arsenide substrate. Owing to the self-similarity of fractal structures, our fractal antenna shows a multiband emission of terahertz radiation. The emission intensity at peak frequency is about twice that from a bow-tie antenna. We also investigate the mechanism of the multiband emission by using the finite-difference time-domain calculation.

Characterization of CdTe, Cd xZn 1−xTe and GaAs detectors

We report space-and-time current spectroscopy for characterization of high-quality GaAs thin films grown on semi-insulating gallium arsenide substrates. The approach is based on illumination of semiconductor material with an oscillating interference pattern formed of two light waves, one of which is phase modulated with frequency ω. The non-steady-state photocurrent flowing through the short-circuited semiconductor is the measurable quantity in this technique. The alternating current resulted from the periodic relative shifts of the photoconductivity and space charge electric field gratings arising in the crystal's volume under illumination. The results of measurements of semiconductor material's parameters of CdTe and Cd x Zn 1− x Te detectors are presented. The experiments are carried out for the diffusion regime of signal excitation at light wavelength λ=1.15 μm. The sign, conductivity and diffusion length are estimated from the dependencies of the signal on the temporal and spatial frequencies. The high-quality GaAs thin films grown on semi-insulating gallium arsenide substrates are characterized. The experiments are carried out in the geometry of the Michelson interferometer at the illumination wavelength of 532 nm. The dependence of the non-steady-state photocurrent on spatial frequency of the interference pattern is measured, allowing estimation of the diffusion length of photoelectrons in GaAs thin film L D=40 μm.

Space-and-time current spectroscopy of GaAs-based detectors

We report space-and-time current spectroscopy for characterization of high-quality GaAs thin films grown on semi-insulating gallium arsenide substrates. The approach is based on illumination of semiconductor material with an oscillating interference pattern formed of two light waves, one of which is phase modulated with frequency ω. The non-steady-state photocurrent flowing through the short-circuited semiconductor is the measurable quantity in this technique. The alternating current is resulted from the periodic relative shifts of the photoconductivity and space charge electric field gratings, which arise in the crystal's volume under illumination. The experiments are carried out in the geometry of Michelson interferometer at the illumination wavelength of 532 nm. The dependence of the non-steady-state photocurrent on spatial frequency of the interference pattern is measured allowing estimation of the diffusion length of photoelectrons in GaAs thin film L D=40 μm.

High-Q factor three-dimensional inductors

In this paper, the great flexibility of three-dimensional (3-D) monolithic-microwave integrated-circuit technology is used to improve the performance of on-chip inductors. A novel topology for high-Q factor spiral inductor that can be implemented in a single or multilevel configuration is proposed. Several inductors were fabricated on either silicon substrate (/spl rho/ = 30 /spl Omega/ /spl middot/ cm) or semi-insulating gallium-arsenide substrate demonstrating, more particularly, for GaAs technology, the interest of the multilevel configuration. A 1.38-nH double-level 3-D inductor formed on an Si substrate exhibits a very high peak Q factor of 52.8 at 13.6 GHz and a self-resonant frequency as high as 24.7 GHz. Our 4.9-nH double-level GaAs 3-D inductor achieves a peak Q factor of 35.9 at 4.7 GHz and a self-resonant frequency of 8 GHz. For each technology, the performance limits of the proposed inductors in terms of quality factor are discussed. Guidelines for the optimum design of 3-D inductors are provided for Si and GaAs technologies.

Response of semi-insulating GaAs detectors to near-infrared picosecond light pulses

Semi-insulating gallium arsenide (SI-GaAs) detectors, in the form of Schottky diodes, have been irradiated from the front or from the back contact or from the side, with light pulses from picosecond laser source, tunable in the range of 780–1020 nm and focused to a 50–100 μm spot on the surface of the detector. Energy per pulse was in the range of 4–25 pJ, with a 10 or 100 Hz repetition rate. Each pulse mimics the interaction of a single energetic particle with the substrate, but with a photon mean free path modulated in the range of 1 μm–1 cm, depending on the light wavelength. The SI-GaAs substrates have a thickness of 200 μm (VGF grown), or 600 μm (LEC) or 1000 μm (VGF). The time response of the detectors, analysed with the Transient Current Technique (using a fast digital sampling oscilloscope) in terms of peak signal amplitude and charge rise time, has been evaluated as a function of: reverse voltage bias (50–1200 V), light wavelength (780–1020 nm), side position between the electrodes, position on the front contact. The results are: (1) the shape of the transient current signal may show the presence of two peaks, about 1 ns apart; (2) the charge rise time, considered to be dominated by the charge collection time, is between 2 and 13 ns; (3) the charge rise time, as due to electron drift or hole drift in the region between the contacts, has been measured as 2–5 ns, also dependent on the applied bias; (4) the transient current (exponential) decay time, for front or back irradiation, increases with the bias voltage up to 2–20 ns and these data are considered to be consistent with the electron detrapping time; (5) under reverse bias, for 1 mm pad side and a large ohmic contact on the back, the electric field extends around the front contact up to about 200 μm.

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.

Experimental investigation of microwave-optoelectronic interactions in a microstrip ring resonator

Microwave optoelectronic mixing on a semi-insulating gallium arsenide substrate performed by monolithically integrating Schottky diode photodetectors into a microstrip ring resonator is discussed. When operated in the resistive mixing mode, a low frequency difference signal is extracted from the bias pad of the circuit. In the parametric mode, both degenerate and non-degenerate parametric amplification of an optical carrier signal takes place. The circuit shows good potential for application in wide-band fiberoptic systems. >

Semi-insulating gallium arsenide substrates for high-frequency FET and IC fabrication : Harvey Winston. Solid St. Technol., 145 (January 1983)

Semi-insulating gallium arsenide substrates for high-frequency FET and IC fabrication : Harvey Winston. Solid St. Technol., 145 (January 1983)

High-speed GaAs SDFL divider circuit

High-speed divider circuits find numerous applications in prescalers for counters, frequency synthesizers, and digital phase locked loops. To accommodate these applications, a high-speed multimode divider circuit has been designed, fabricated, and tested. This circuit, fabricated on semi-insulating Gallium Arsenide substrates, and utilizing Schottky diode FET logic (SDFL) technology, has been tested at a maximum clock frequency of 1.84 GHz. High yields of circuits operating over 1 GHz have been obtained over a number of wafers.

High-Speed GaAs SDFL Divider Circuit

High-speed divider circuits find numerous applications in prescalers for counters, frequency synthesizers, and digital phase locked loops. To accommodate these applications, a high-speed multimode divider circuit has been designed, fabricated, and tested. This circuit, fabricated on semi-insulating Gallium Arsenide substrates, and utilizing Schottky diode FET logic (SDFL) technology, has been tested at a maximum clock frequency of 1.84 GHz. High yields of circuits operating over 1 GHz have been obtained over a number of wafers.

Properties of Interconnection on Silicon, Sapphire, and Semi-Insulating Gallium Arsenide Substrates

Interconnection capacitances and inductances on oxide-passivated silicon, sapphire, and semi-insulating gallium arsenide substrates were calculated and compared. The results showed that, including coupling effects, the capacitances on insulating substrates are lower only at large Iinewidths, but become comparable to values on silicon substrates at linewidths below 2.5 /spl mu/m. The frequency-dependent nature of inductances on silicon substrates was reviewed. The results indicated that, at frequencies where most digital integrated circuits operate, silicon substrates can be treated as a lossless medium. Hence, inductances on silicon substrates can be calculated by the same means as on insulating substrates. The propagation delay of an interconnection resulting from using different substrates was also evaluated. It can be shown that for VLSI development the choice of substrates is not nearly as critical as the problem of series resistance of an interconnection.

Properties of interconnection on silicon, sapphire, and semi-insulating gallium arsenide substrates

Interconnection capacitances and inductances on oxide-passivated silicon, sapphire, and semi-insulating gallium arsenide substrates were calculated and compared. The results showed that, including coupling effects, the capacitances on insulating substrates are lower only at large linewidths, but become comparable to values on silicon substrates at linewidths below 2.5 µm. The frequency-dependent nature of inductances on silicon substrates was reviewed. The results indicated that, at frequencies where most digital integrated circuits operate, silicon substrates can be treated as a lossless medium. Hence, inductances on silicon substrates can be calculated by the same means as on insulating substrates. The propagation delay of an interconnection resulting from using different substrates was also evaluated. It can be shown that for VLSI development the choice of substrates is not nearly as critical as the problem of series resistance of an interconnection.