J. Antoszewski

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.

Magneto-transport characterization using quantitative mobility-spectrum analysis

A quantitative mobility spectrum analysis (QMSA) of experimental Hall and resistivity data as a function of magnetic field is presented. This technique enables the conductivity contribution of bulk majority carriers to be separated from that of other species such as thermally generated minority carriers, electrons, and holes populating n and p doped regions, respectively, and two-dimensional species at surfaces and interface layers. Starting with a suitable first trial function such as the Beck and Anderson mobility spectrum analysis (MSA), a variation on the iterative procedure of Dziuba and Gorska is used to obtain a mobility spectrum which enables the various carrier species present in the sample to be identified. The QMSA algorithm combines the fully automated execution and visually meaningful output format of MSA with the quantitative accuracy of the conventional least-squares multi-carrier fitting procedure. Examples of applications to HgCdTe infrared detector materials and InAs/GaSb quantum wells are discussed. The ultimate goal of this paper is to provide an automated, universal algorithm which may be used routinely in the analysis and interpretation of magneto-transport data for diverse semiconductor materials and bandgap engineered structures.

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.

Vertical minority carrier electron transport in p-type InAs/GaSb type-II superlattices

Vertical minority carrier electron transport parameters in p-type InAs/GaSb type-II superlattices for long wavelength infrared (LWIR) detection have been extracted from magnetic field dependent geometrical magneto-resistance. The measurements, performed at low electric fields and at magnetic field intensities up to 12 T, exhibited multiple-carrier conduction characteristics that required mobility spectrum analysis for the extraction of individual carrier mobilities and concentrations. Within the common operating temperature range for LWIR photodiodes (80 to 150 K), the conductivity was found to be dominated by three distinct carriers, attributed to majority holes (μ=280±27 cm2/Vs), minority electrons (μ=2,460±75 cm2/Vs), and parasitic sidewall inversion layer electrons (μ=930±55 cm2/Vs). A miniband energy gap of 140 ± 15 meV for the 14/7-monolayer InAs/GaSb superlattice was estimated from the thermal activation of the minority carrier electron density.

A novel multi-heterojunction HgCdTe long-wavelength infrared photovoltaic detector for operation under reduced cooling conditions

A new multi-heterojunction photovoltaic infrared photodetector is presented. The device has been developed specifically for operation at elevated temperatures for detection of infrared radiation in the mid- and long-wavelength range of the infrared spectrum. The new structure solves the perennial problems of poor quantum efficiency and low dynamic resistance found in conventional long-wavelength infrared photovoltaic detectors when operated near room temperature. Analysis indicates that practical devices with properly optimized multiple heterojunction layers are capable of achieving the performance limits imposed by the statistical nature of thermal generation-recombination processes. In order to demonstrate the technology, multiple heterojunction devices have been fabricated on epilayers grown by isothermal vapour phase epitaxy of HgCdTe and in situ As p-type doping. The detector structures were formed using a combination of conventional dry etching, angled ion milling and angled thermal evaporation for contact metal deposition. These multi-junction HgCdTe heterostructure devices exhibit performances comparable to, or better than, existing long-wavelength photoconductors and photoelectromagnetic detectors operated under the same conditions. A typical of optically immersed multiple heterostructure photovoltaic detectors of approximately can be achieved at a signal wavelength of and for operation at 230 K.

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.

Environmental stability and cryogenic thermal cycling of low-temperature plasma-deposited silicon nitride thin films

Stress in low-temperature plasma-enhanced chemical vapor deposited silicon nitride (SiNx) thin films subject to cryogenic thermal cycling (100–323K) has been measured. It is observed that the SiNx deposition temperature strongly influences the thin film characteristics. For films deposited between 200 and 300°C, the thermal expansion coefficient is similar to that of silicon over the 180–323K temperature range. The room temperature thermal expansion coefficient of SiNx films is found to decrease sublinearly from 5.2×10−6to2.6×10−6K−1 as the temperature of the deposition process is increased from 50to300°C. The negative correlation between deposition temperature and thin film thermal expansion coefficient, and the positive correlation between deposition temperature and the thin film Young’s modulus inferred from nanoindentation are postulated to be associated with the local bonding environment within the thin film. The stress state of SiNx films deposited above 150°C is stable under atmospheric conditions,...

Mercury annealing of reactive ion etching induced p- to n-type conversion in extrinsically doped p-type HgCdTe

Mercury annealing of reactive ion etching (RIE) induced p- to n-type conversion in extrinsically doped p-type epitaxial layers of HgCdTe (x=0.31) has been used to reconvert n-type regions created during RIE processing. For the RIE processing conditions used (400 mT, CH4/H2, 90 W), p- to n-type conversion was observed using laser beam induced current (LBIC) measurements. After a sealed tube mercury anneal at 200 °C for 17 h, LBIC measurements clearly indicated that no n-type converted region remained. Subsequent Hall measurements confirmed that the material consisted of a uniform p-type layer, with electrical properties equivalent to that of the initial as-grown wafer (NA−ND=2×1016 cm−3, μ=350 cm2 V−1 s−1).

Characterization of carriers in GaSb∕InAs superlattice grown on conductive GaSb substrate

We report on mobility spectrum analysis of electrical transport in a GaSb∕InAs superlattice (SL) grown on GaSb substrate. Despite domineering contribution to conduction from the substrate, it was possible to discern and characterize carriers from SL. A single electron specie with an ambient temperature mobility of ∼104cm2∕Vs was found to emanate from SL. We show that this carrier has an activation energy of 0.27eV and is associated with the SL band gap.