L. Faraone

Scattering mechanisms limiting two-dimensional electron gas mobility in Al0.25Ga0.75N/GaN modulation-doped field-effect transistors

In order to characterize the electron transport properties of the two-dimensional electron gas (2DEG) in AlGaN/GaN modulation-doped field-effect transistors, channel magnetoresistance has been measured in the magnetic field range of 0–12 T, the temperature range of 25–300 K, and gate bias range of +0.5 to −2.0 V. By assuming that the 2DEG provides the dominant contribution to the total conductivity, a one-carrier fitting procedure has been applied to extract the electron mobility and carrier sheet density at each particular value of temperature and gate bias. Consequently, the electron mobility versus 2DEG sheet density has been obtained for each measurement temperature. Theoretical analysis of these results suggests that for 2DEG densities below 7×1012 cm−2, the electron mobility in these devices is limited by interface charge, whereas for densities above this level, electron mobility is dominated by scattering associated with the AlGaN/GaN interface roughness.

Monolithic integration of an infrared photon detector with a MEMS-based tunable filter

The monolithic integration of a low-temperature microelectromechanical system (MEMS) and HgCdTe infrared detector technology has been implemented and characterized. The MEMS-based tunable optical filter, integrated with an infrared detector, selects narrow wavelength bands in the range from 1.6 to 2.5 /spl mu/m within the short-wavelength infrared (SWIR) region of the electromagnetic spectrum. The entire fabrication process is compatible with two-dimensional infrared focal plane array technology. The fabricated device consists of an HgCdTe SWIR photoconductor, two distributed Bragg mirrors formed of Ge-SiO-Ge, a sacrificial spacer layer within the cavity, which is then removed to leave an air gap, and a silicon nitride membrane for structural support. The tuning spectrum from fabricated MEMS filters on photoconductive detectors shows a wide tuning range, and high percentage transmission is achieved with a tuning voltage of only 7.5 V. The full-width at half-maximum ranged from 95 to 105 nm over a tuning range of 2.2-1.85 /spl mu/m.

Quantitative mobility spectrum analysis of multicarrier conduction in semiconductors

We demonstrate an optimized quantitative mobility spectrum analysis (QMSA) technique for determining free electron and hole densities and mobilities from magnetic-field-dependent Hall and resistivity data. The procedure is applied to an In1−xGaxAs–In1−xAlxAs single quantum well, GaAs–AlAs asymmetric double quantum wells, and Hg1−xCdxTe epitaxial thin films containing multiple carrier species. The results illustrate the reliability, versatility, and sensitivity of the analysis, which is fully computer automated following input of the magnetic-field-dependent data. QMSA is found to be a suitable standard tool for the routine electrical characterization of semiconductor material and device transport properties.

Effects of partially occupied sub-bands on two-dimensional electron mobility in AlxGa1−xN/GaN heterostructures

In this article we present a study of the effect that partial occupancy of sub-bands on the two-dimensional electron mobility at different temperatures, using a fully numerical calculation in unintentionally doped AlxGa1−xN/GaN heterostructures with different Al mole fraction in the AlxGa1−xN barrier. The analysis of our results clearly indicates that the effect of partial sub-band occupancy be considerable, especially at higher temperatures and higher Al mole fractions when more than one sub-band is occupied. Comparison of our calculated results with published experimental data shows good agreement.

MAGNETIC FIELD DEPENDENT HALL DATA ANALYSIS OF ELECTRON TRANSPORT IN MODULATION-DOPED ALGAN/GAN HETEROSTRUCTURES

Experimental magnetic field dependent Hall and resistivity data is presented for two modulation-doped AlGaN/GaN heterostructures in the temperature range from 6 to 300 K and for a magnetic field up to 12 T. The mobility and concentration of electrons within the two-dimensional electron gas (2DEG) at the AlGaN/GaN interface and within the underlying GaN layer are readily separated and characterized using quantitative mobility spectrum analysis. The observed transport parameters of the 2DEG are explained using the classical band theory for a degenerate electron gas. Analysis of the temperature dependencies of mobility and electron concentration in the GaN layer and 2DEG indicates that electron transport in the GaN layer is dominated by carriers in the conduction band for the case of low-doping ( 1018 cm−3). The simultaneous analysis of the multilayer AlGaN/GaN structure applied in this work renders the results applicable directly...

Optical characterization of Fabry-Pe/spl acute/rot MEMS filters integrated on tunable short-wave IR detectors

Optical characterization of a microspectrometer based on a voltage tunable Fabry-Pe/spl acute/rot microelectromechanical optical filter monolithically integrated on a Hg/sub x/Cd/sub 1-x/Te infrared (IR) photoconductor is presented. Wavelength tuning from 1.7 to 2.35 /spl mu/m (650 nm) with less than 9 V is demonstrated. Bandwidths of less than 55/spl plusmn/5 nm and switching times of 60/spl plusmn/10 /spl mu/s have been achieved. Requirements to reduce the optical bandwidth and extend the tunable range are discussed. This technology has potential applications in hyperspectral imaging and spectroscopy across the entire IR band from 1 to 12 /spl mu/m.

Diffusion length measurements in p-HgCdTe using laser beam induced current

The minority carrier diffusion length in p-HgCdTe is a key indicator of material quality and gives an indication of n-on-p diode performance when the zero bias resistance is diffusion limited. We present results of a temperature dependent study of diffusion length in p-HgCdTe using laser beam induced current (LBIC). Carriers are collected by a p-n junction formed using standard diode junction formation conditions, and thus not necessarily extending to the substrate. Two-dimensional modeling is used to examine the validity of results obtained using this geometry, as compared to the more standard diffusion length test structure geometries, which are harder to fabricate. The temperature dependence of the diffusion length can be compared with theoretical models to determine the dominant recombination mechanisms.

Hydrogenation of ZnS passivation on narrow-band gap HgCdTe

Due to the narrow band gap of HgCdTe required for infrared photodetectors, the device performance is readily influenced by surface effects. This letter examines the effect that hydrogenation has on the quality of industry-standard ZnS passivating films. The hydrogenation is achieved by exposing the samples to a H2/CH4 plasma that is present during a reactive ion etching process. The results show a marked improvement of the passivant/substrate interface for hydrogenated devices with a reduction of the average fixed interface charge density to 3.5×1010 cm−2, accompanied by a sixfold decrease in the standard deviation. The advantage of this method of hydrogenation is that it is integrated into the reactive ion etch processing for mesa formation or p-type to n-type conversion in photoconductive or photovoltaic device fabrication, respectively. With the improvement of the ZnS passivation with hydrogenation, this method may alleviate the need for complex epitaxial passivation processing.

Analysis of magnetic field dependent Hall data in narrow bandgap Hg1−xCdxTe grown by molecular beam epitaxy

The analysis of magnetic field dependent Hall data is presented for three representative Hg1−xCdxTe layers grown by Molecular Beam Epitaxy with x in the range 0.193 to 0.244. These samples exhibit ‘‘anomalous’’ Hall characteristics which are analyzed using a hybrid approach consisting of mobility spectrum (MS) analysis followed by a multi‐carrier fitting (MCF) procedure. This hybrid approach is able to readily separate contributions to the total conductivity arising from extrinsic carriers, thermally activated intrinsic electrons, and two‐dimensional electron layers. The extracted transport parameters for thermally activated intrinsic electrons are shown to be in excellent agreement with established physical models for narrow bandgap HgCdTe. The two‐dimensional electron layers are found to be only weekly temperature dependent with an electron mobility in the range of 2 to 4×104 cm2/V s and a sheet density in the range of 1011 to 1012 cm−2. Of particular interest, is the fact that the ‘‘anomalous’’ Hall ch...

High Resolution Mobility Spectrum Analysis of Multicarrier Transport in Advanced Infrared Materials

In this paper the recently developed high-resolution mobility spectrum analysis is demonstrated. In a number of simulations the high resolution of the algorithm is demonstrated in the high and low mobility ranges. The effect of random noise, maximum magnetic field limit, and the number of magnetic field points used in the experiment is also demonstrated. Also discussed are requirements critical for obtaining high-quality experimental data. The application of this new algorithm to complex semiconductor structures to study lateral and vertical transport is also demonstrated, resulting in insight into previously unavailable details.