Investigation of InAsSbP quantum dot mid-infrared sensors

This work presents the results of investigations of a low bias mid-infrared(IR) photoconductive cell (PCC) with InAsSbP quantum dots (QDs). The self-assembled nanostructures were grown on an InAs(100) substrate by modified liquid phase epitaxy. The coarsening of the QDs due to Ostwald ripening was discussed. Hysteresis with a remnant capacitance of 0.483 pF and contra-directional oscillations on the PCC's capacitance–voltage characteristic at 78 K were observed. Additionally, peaks at 3.48, 3.68 and 3.89 μm on the room temperature photoresponse spectrum of a quantum dot photoconductive cell were detected. Room temperature photo-sensing properties were investigated under an irradiation of 3.39 μm as well. At a power density of 0.07 W cm−2, the surface resistance of quantum dot PCC was reduced by up to 7 %. A current responsivity of 0.2 mA W−1 was measured at an applied voltage of 8 mV.

The Influence of GaSb Layer Thickness on the Band Gap of InAs/GaSb Type-II Superlattices for Mid-Infrared Detection

ABSTRACTThe effect of small changes in GaSb layer thickness on the photoresponse spectrum of InAs/GaSb superlattices (SLs) designed for mid-infrared detection was systematically investigated. The samples were grown by molecular beam epitaxy with precisely calibrated growth rates. The basic SL used for this study consisted of 40 periods of InAs (20.5 Å)/GaSb (X Å), where the nominal value for X was adjusted from 18 to 27 Å in four different samples. An InSb-like interface (IF) was inserted between the layers to balance the SL strain. By decreasing the GaSb width, the photoresponse cut-off wavelength (λc) was adjusted from 4.03 μm to 4.55 μm, i.e., the SL energy band gap is being decreased. This decrease in the energy separation between the first heavy hole band (HH1) and the first conduction band (C1) as the GaSb layer is narrowed is counter intuitive. However, this experimental trend can be explained by a modified envelope function approximation (EFA) calculation that includes the effect of in-plane asymmetry at InAs/GaSb interfaces. As expected, the HH band is pushed away from the top of the GaSb valence band as the GaSb layer width becomes narrower. However, at the same time the C1 band is significantly broadened by the increased wave function overlap of the electron states in the InAs layer. The trend to smaller band gap with narrower GaSb layers and other effects of the design changes on the photoresponse spectrum are discussed.

Study on preparation, growth mechanism, and optoelectronic properties of highly oriented WSe2 thin films

Recently, highly oriented WSe2 thin films, with the c axis of the crystallites perpendicular to the substrate, were reproducibly obtained by interposing a Ni/Cr thin layer between the substrate and a WO3 precursor film. In the present work the preparation conditions were varied to elucidate the growth mechanism of such films. A model for the growth mode is proposed. Based upon this analysis, WSe2 thin films with improved crystalline and electronic properties were obtained. The photoresponse spectrum for photoelectrochemical cells with the WSe2 electrode immersed into a selenosulfate solution was measured. Quantum efficiency of 0.1% was calculated from this spectrum.

Long Wavelength Shifting and Broadening of Quantum Well Infrared Photodetector Response Via Rapid Thermal Annealing

A shift in the peak response wavelength and a broadening of the photoresponse spectrum is demonstrated for intersubband absorption in n-doped GaAs/AIGaAs multiple quantum well detectors following intermixing of the well and barrier layers during rapid thermal annealing. In general, a decrease in performance is observed for the RTA QWIPs when compared to the as-grown detectors. The peak absolute response of the annealed QWIPs is lower by almost a factor of four, which results in corresponding decrease in quantum efficiency. In addition, the noise performance results in a detectivity which is five times lower than that of QWIPs fabricated from as-grown structures.