Results are presented for a dual-band detector that simultaneously detects UV radiation in the 250-360 nm and IR radiation in the 5-14 microm regions with near zero spectral cross talk. In this detector having separate UV- and IR-active regions with three contacts (one common contact for both regions) allows the separation of the UV and IR generated photocurrent components, identifying the relative strength of each component. This will be an important development in UV-IR dual-band applications such as fire-flame detection, solar astronomy, and military sensing, eliminating the difficulties of employing several individual detectors with separate electronics-cooling mechanisms.

Oblique-angle deposited titanium dioxide (TiO(2)) nanorods have attracted much attention as good antireflection (AR) coating material due to their low n profile. Therefore, it is necessary to better understand the optical properties of these nanorods. TiO(2) nanorods grown on glass and Si substrates were characterized in the visible (0.4-0.8 μm) and infrared (2-12 μm) regions to extract their complex n profiles empirically. Application of these nanorods in multilayer AR coatings on infrared detectors is also discussed. Optimization of graded index profile of these AR coatings in the broad infrared region (2-12 μm) even at oblique angles of incidence is discussed. The effective coupling between the incoming light and multiple nanorod layers for reducing the reflection is obtained by optimizing the effect from Fabry-Perot oscillations. An optimized five-layer AR coating on GaN shows the reflectance less than 3.3% for normal incidence and 10.5% at 60° across the whole 2-8 μm spectral range.

The optical properties of p-type InP epitaxial films with different doping concentrations are investigated by infrared absorption measurements accompanied by reflection and transmission spectra taken from 25 to 300 K. A complete dielectric function (DF) model, including intervalence band (IVB) transitions, free-carrier and lattice absorption, is used to determine the optical constants with improved accuracy in the spectral range from 2 to 35 μm. The IVB transitions by free holes among the split-off, light-hole, and heavy-hole bands are studied using the DF model under the parabolic-band approximation. A good understanding of IVB transitions and the absorption coefficient is useful for designing high operating temperature and high detectivity infrared detectors and other optoelectronic devices. In addition, refractive index values reported here are useful for optoelectronic device designing, such as implementing p-InP waveguides in semiconductor quantum cascade lasers. The temperature dependence of hole effective mass and plasma frequency is also reported.

Capacitance characteristics with voltage and frequency of n+-GaN/AlxGa1−xN heterojunction ultraviolet (UV)-infrared (IR) photodetectors are reported. A distinct capacitance step and capacitance hysteresis have been attributed to trap energy states located just above the Fermi level at the GaN/AlGaN interface, most likely due to N-vacancy and/or C-donor impurities. The presence of the hysteresis is due to the accumulation of charge at the heterointerface, which is dependent on the location of the continuum of interface trap states relative to the Fermi level. The Al fraction in the barrier layer has been found to significantly change the positions of the interface trap states relative to the Fermi level.

Abstract-A heterojunction interfacial workfunction internal photoemission (HEIWIP) terahertz detector with ∼1×1018 cm −3 n-type doped GaAs emitters in a multilayer GaAs/Al 0.13 Ga 0.87 As heterostructure is presented. The detection mechanism is based on free carrier absorption with a broad response extending to ∼5.26 THz (57 μm), corresponding to an effective workfunction of ∼21.8 meV, which is much smaller than the offset expected for an Al fraction of x = 0.13 at a 1 × 10 18 cm −3 doping. This is attributed to a reduction of the conduction band offset by interface dipole formation between the accumulated negative charges at the interface states and migrated positively charged donors in the barrier. The device has a peak responsivity of 0.32 A/W at ∼26 μm at 5 K. It is demonstrated that the dopant migration-induced interface dipole effect can be used to extend the zero response threshold frequency (f 0 ) of n-type HEIWIP detectors.