A nanoimprinting method was used to generate square imprints and arrays of imprints ranging in lateral dimension from 1 mu m to 50 mu m in p-type HgCdTe. Laser Beam Induced Current (LBIC) characterization shows electrical type conversion around each imprint and imprint array. The LBIC signal intensity surface maps of imprinted regions and their dependence with measurement temperature correspond well with surface maps of n-on-p HgCdTe photodiodes formed by conventional techniques. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3582062]

Results of photoresponse measurements performed on long-wave infrared photoconductors fabricated from HgTe-HgCdTe superlattices grown by molecular beam epitaxy are presented. Absolute spectral photoresponse measurements as a function of temperature and applied electric field have be undertaken, with the peak photoresponse of 3.3×103 V/W measured at 100 K. Sweepout effects were observed for fields greater than 20 V/cm and quantum efficiencies approaching 80% for 5 μm thick devices have been predicted from absorption measurements of grown material.

Erratum: N2-Based Thermal Passivation of Porous Silicon to Achieve Long-Term Optical Stability [Electrochem. Solid-State Lett., 13, H428 (2010)] T. D. James, Meifang Lai, G. Parish, C. A. Musca, and A. J. Keating Microelectronics Research Group, School of Electrical, Electronic, and Computer Engineering, and Sensors and Advanced Instrumentation Laboratory, School of Mechanical Engineering, The University of Western Australia, Crawley, Western Australia 6009, Australia

We report supporting evidence that is consistent with p- to n-type conversion of HgCdTe that is induced by surface indentation, as the progress towards the fabrication of photovoltaic infrared detectors by direct imprinting.

A technique is presented to create porous silicon (PS) thin films with long-term optical stability when exposed to normal room conditions. This technique requires the thin films to undergo a rapid thermal annealing treatment at a relatively low temperature of 600 degrees C in N-2 atmosphere for 6 min. Annealing at such a low temperature enables the surface passivation of PS via nitridation without causing the excessive roughness and sintering widely observed at higher annealing temperatures. A mechanism similar to the Haber process is proposed to explain the surface nitridation, in which the nitrogen atmosphere interacts with the as-anodized hydrogen surface species. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3489075] All rights reserved.

Optical measurements of thin-film-stress-induced substrate bending have been employed in a characterization of long-term environmental stability of stress of low-temperature (<125°C) plasma enhanced vapor deposited (PECVD) SiNx, as well as thermally evaporated SiOx, and Ge thin films for applications in micro-electro-mechanical systems (MEMS) fabricated on temperature sensitive, non-standard substrates. It has been found that in comparison to their stress values measured at atmospheric conditions, PECVD SiNx layers prepared below ∼100°C as well as layers of thermally evaporated Ge exhibit significantly more tensile (less compressive) stress values when measured in vacuum, which are reversible upon re-exposure to an atmospheric, dry nitrogen, helium, argon, or oxygen ambient. Raising the deposition temperature above ∼100°C results in PECVD SiNx stress being stable in vacuum and dry nitrogen storage, which is complemented by stress stability in laboratory atmosphere for films deposited above ∼125°C. Stress of thermally evaporated SiOx layers is stable in vacuum and undergoes compressive stress development in either dry nitrogen or laboratory air.

A technique is presented for the passivation of porous silicon (PS) thin films via nitrogen based annealing at the lowest temperature ever reported. Annealing freshly anodized PS thin films at temperatures as low as 520 degrees C under N-2 flow in a rapid thermal annealer produces films that show no change in refractive index when exposed to ambient conditions over 60 days. These films also exhibited chemical resistance by surviving a brief dip in both concentrated KOH and buffered HF. Unlike most other PS surface passivation methods, this technique causes negligible reduction in refractive index of the annealed PS thin films. Passivation only occurs when dangling bonds and mono-hydrides populate the PS surface, providing a path for thermal interactions with the N-2 gas. (C) 2009 Elsevier Ltd. All rights reserved.

We present a technique involving the use of pulsed anodization for porous silicon (PS) thin-film fabrication on low doped substrates, for which the interface roughness and porosity gradients usually observed in such films can be eliminated. The work presented includes a detailed characterization of the effects of duty cycle and frequency during pulsed anodization. The study spans pulsing frequencies of 0.1-1000 Hz and duty cycles of 5-50%. The combination of low frequency (0.1 Hz) and low duty cycle (5%) for the pulse train used for anodization produces PS thin films, displaying no measurable interface roughness or porosity gradient. The mechanisms behind the wide variation in available PS thin-film properties with pulsed anodization parameters are analyzed using a galvanostatic technique. The analysis indicates that the inhomogeneity and roughness observed in PS films fabricated on low doped starting wafers are both due to the unstable multistep dissolution kinetics of silicon during PS film formation.

This is the first report of photovoltaic detectors fabricated by direct imprinting of a semiconductor. Evidence is reported that is consistent with the indented region of p-type HgCdTe type converted to n-type HgCdTe.

Nanoindentation has been utilised in order to investigate the mechanical properties of low-temperature (50-300 degrees C) plasma-dcposited SiNx thin films for applications of micro-electro-mechanical systems on temperature sensitive, non-standard substrates. It is found that films deposited at higher temperatures are suitable for these applications, in contrast to films deposited at lower temperatures which tend to have much lower values of Young's modulus and hardness, as well as exhibit significant surface roughness, porosity, and creep. The correlation of SiNx mechanical properties with deposition temperature is shown to be associated with thin film atomic composition and details of the deposition process.

The materials and processes for fabrication of monolithically integrated microelectromechanical systems-based microspectrometers operating in the short-wavelength IR range is presented. Using low-temperature surface micromachining techniques, compatible with a range of IR sensor technologies, silicon-nitride-based tunable Fabry-Perot filter structures with distributed Bragg mirrors made of Ge/SiO/Ge layers have been monolithically integrated with HgCdTe photoconductors. The stress within and between the many layers of the structure has been eliminated or compensated by stress tuning of the deposition conditions. The demonstrated microspectrometers have a tuning range of 1.8-2.2 mu m with relative peak transmission of 70% and full-width at half-maximum of 80 +/- 10 nm.

The production of high quality optical devices based on porous silicon relies on having precise control over the refractive index and thickness of each porous silicon layer. Until now this has been achieved by pre-calibrating each growth system and making sure that parameters such as wafer doping, electrolyte concentration and temperature are kept constant with each fabrication. However low doped silicon required for IR based silicon photonics has significant non-uniformity in the index and growth rate during formation of the porous silicon. The solution we have developed is based on realtime in-situ monitoring of low-doped silicon during porous silicon growth. This process rapidly measures the optical interference between the porous silicon film and the backside silicon surface. The optical light source comes from six coarse-wavelength-division-multiplexed lasers, with rapid switching between wavelengths achieved using a microelectromechanical switch. The system permits rapid measurement (<1 sec) of the reflection spectra from all lasers, enabling real-time thickness and refractive index of each layer to be determined during growth. Our aim is to enable growth of high quality multi-layer films such as those required for Bragg Reflectors and high-Q Fabry-Perot microcavities. In this paper we briefly describe the instrument, the numerical models developed to gather the measurements, and show preliminary results gathered from this instrument during growth. The results show a good agreement with theoretical optical modelling, and also direct measurements of the porous silicon layers.

Arsenic incorporation in HgTe∕Hg0.05Cd0.95Te superlattices grown by molecular beam epitaxy (MBE) is reported. The incorporation was carried out by a δ-doping approach where arsenic was incorporated during MBE growth as acceptors. The superlattices were characterized via high resolution x-ray diffraction, Fourier transform infrared spectroscopy, secondary ion mass spectrometry, and magnetotransport Hall measurements coupled with the quantitative mobility spectrum analysis algorithm.

Microspectrometers based on the monolithic integration of a microelectromechanical system (MEMS) Fabry–Pérot filter and a Hg x Cd1–x Te-based infrared detector are discussed and measured results presented. The microspectrometers are designed to operate in the 1.5 μm to 2.6 μm wavelength range. Design equations are presented which account for the mechanical and optical characteristics of the device. Measurements indicate linewidths as narrow as 55 nm, switching times of 40 μs, and a tuning range of 380 nm, which is limited by snap-down. Optical characterization of the distributed Bragg mirrors and the Fabry–Pérot filter are presented, and these are shown to be in good agreement with simple first-order analytical models. Bowing of the movable Fabry–Pérot mirror due to stress gradients is identified as the dominant source of linewidth broadening.

Research into p-type doping of HgCdTe with arsenic has concentrated on the use of a conventional effusion cell and optimization of growth conditions to achieve an increase in incorporation efficiency. This study investigates the use of a cracker cell, which is now the preferred method of doping HgCdTe due to its higher arsenic incorporation efficiency under optimum growth conditions. A detailed investigation of a number of arsenic doped HgCdTe layers grown on CdZnTe substrates by molecular beam epitaxy using a cracker cell as a source of arsenic is presented. Growth parameters influencing the amount of arsenic incorporated, such as the cracker-cell bulk temperature and substrate temperature, were investigated. Arsenic depth profiles were obtained via detailed secondary ion mass spectrometry where all major constituents in the epilayers were analysed. Magneto-transport Hall measurements were performed on as-grown material and those that underwent high-temperature anneals typical for arsenic activation. Using the quantitative mobility spectrum analysis technique, contributions to total conductivity arising from various carriers present in the samples have been separated. As-grown samples were found to exhibit n-type behaviour consistent with arsenic incorporating on cation sublattice, while samples that underwent high-temperature annealing show partial activation of arsenic with electron compensation.

To determine a suitable passivation and insulation layer for HgCdTe photodiodes, the properties of various low temperature plasma-enhanced chemical vapour deposition (PECVD) SiN films were investigated. Metal-insulator-metal (MIM) capacitors were fabricated on silicon to determine a suitable PECVD SiN film for insulation of HgCdTe diodes. It was found that PECVD process temperature of 125degC, at high power, and low process pressure gave the best film characteristics. These films were stable in atmosphere, as shown by FTIR measurements, which also shows oxidation of low power, high process pressure films. HgCdTe photodiodes were fabricated with PECVD SiN films with 200 W RF power, 300 mTorr pressure, and a SiN4:NH3:N2 5:45:100 gas ratio. Gated diode measurements indicated that R0A values of 3.0times106 Omega cm2 are achievable with fine-tuning of the SiN charge.

HgCdTe is the preferred semiconductor for fabrication of high-performance infrared (IR) detectors. This material also typically contains multiple carrier species for charge, transport, which makes characterisation of the mobility and concentration of each species particularly difficult. Accurate carrier transport characterisation can be achieved by quantitative mobility spectrum analysis of variable-magnetic-field Hall and resistivity data, but this imposes certain conditions concerning sample uniformity and homogeneity. Laser beam induced current (LBIC) is a non-destructive characterisation technique that can be used to qualitatively investigate the electronic properties of HgCdTe samples, specifically including electrically-active defects and p-n junctions. Non-uniformity in the LBIC profiles can also be related to ill-conditioned Hall and resistivity data.