In this letter, we report a quantum well infrared photodetector geometry for normal incidence light coupling. The new optical coupling scheme utilizes total internal reflection at the sidewalls of triangular wires to create favorable optical polarization for infrared absorption. These wires are created by chemically etching an array of V grooves through the detector active region along a specific crystallographic direction. Experimental results from the initial single color as well as two-color detectors with linear wires and unthinned substrate show efficient light coupling comparable to the standard 45° edge coupling, without the undesirable wavelength dependence or spectral narrowing effect of a conventional grating structure. At the same time, the dark current density is substantially reduced due to the partial material removal. Further improvement is expected by creating a two-dimensional coupling structure with substrate thinning.

Articles you may be interested inA gold hybrid structure as optical coupler for quantum well infrared photodetector

We have successfully grown InAs1−xSbx by molecular beam epitaxy over the complete compositional range of 0<x<1 on InAs substrates. The band gaps have been measured using optical absorption and cut-off wavelengths as long as 12.5 μm have been obtained.

We prepared InAs0.02Sb0.98 on semi-insulating GaAs substrates with molecular beam epitaxy and measured the temperature dependence of the band gap. Photoconducting detectors were measured and found to have high internal quantum efficiency (47%) and high speed (10 ns).

We have adopted a binary superlattice structure for long-wavelength broadband detection. In this superlattice, the basis contains two unequal wells, with which more energy states are created for broadband absorption. At the same time, responsivity is more uniform within the detection band because of mixing of wave functions from the two wells. This uniform line shape is particularly suitable for spectroscopy applications. The detector is designed to cover the entire 8 -14 m long-wavelength atmospheric window. The observed spectral widths are 5.2 and 5.6 m for two nominally identical wafers. The photoresponse spectra from both wafers are nearly unchanged over a wide range of operating bias and temperature. The background-limited temperature is 50 K at 2 V bias for F / 1. The past decade has seen increased research activity in the area of broadband quantum-well infrared photodetectors (QWIPs) for spectroscopy in the 8 -14 m atmospheric transmission window.1-6 Development of on-chip infrared spectrometers requires broadband detector material where wavelength-selective pixels are created using structures such as quantum-grid infrared photodetectors or enhanced QWIPs. 7,8 Initial broadband QWIP designs utilized boundto-continuum transitions in multiple QW (MQW) and superlattice (SL) structures.1,2 These detectors had spectral bandwidths ⌬ of ϳ3 m (defined as the full-width at halfmaxima) and peak wavelengths p in the 5 -10 m range. Multistack detectors have also been investigated for broadband as well as voltage tunable multicolor detection.3 Another approach to obtain broadband detection involves MQW structures where each unit consists of several QWs with different well widths and/or well compositions.4-6 Although these structures have ⌬ ϳ 4.5-6 m, large bias voltages are required for obtaining broad response because only the shorter wavelength QWs are turned on at low voltages. Furthermore, since different QWs have different activation energies, their impedance ratio changes with temperature. The resulting change in potential drop leads to different spectral line shapes at different temperatures. In this letter, we present the design and fabrication of long-wavelength broadband QWIPs that employ miniband-to-miniband transitions in binary SL (BSL) structures. These QWIPs have ⌬ ϳ 5-6 m with p ϳ 10 m and exhibit minor changes in bandwidth with bias voltage and temperature.Superlattice detectors were first introduced by Kastalsky et al. 9 Since then, the SL design has been used for both mid-wavelength 10 and long-wavelength 2,11,12 detection. Although these SL detectors have ⌬ ϳ 2-3 m, the responsivity spectra are sharply peaked near their cutoff wavelengths.2,10-12 To further increase the bandwidth and improve the uniformity of the responsivity spectra, we adopted a BSL design. In this structure, the basis of the SL consists of two different wells separated by thin barriers. Upon infrared absorption, electrons from each of the two ground minibands that originate from the two QWs are photoexcited to the two upper mini...