1 Photoluminescence study of long wavelength superlattice infrared detectors Linda Höglund, Arezou Khoshakhlagh, Alexander Soibel, David Z. Ting, Cory J. Hill, Sam Keo, Sarath D. Gunapala Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California, USA 91109-8099 ABSTRACT In this paper, the relation between the photoluminescence (PL) intensity and the PL peak wavelength was studied. A linear decrease of the PL intensity with increasing cut-off wavelength of long wavelength infrared CBIRDs was observed at 77 K and the trend remained unchanged in the temperature range 10 - 77 K. This relation between the PL intensity and the peak wavelength can be favorably used for comparison of the optical quality of samples with different PL peak wavelengths. A strong increase of the width of the PL spectrum in the studied temperature interval was observed, which was attributed to thermal broadening. Keywords: photoluminescence, heterostructure, infrared, photodetector, superlattice, CBIRD, thermal broadening 1. INTRODUCTION Antimony based type-II superlattices (SL) are considered to be one of the main candidates for next generation high performance infrared (IR) detectors. These SLs typically contain alternating thin layers of InAs and GaSb and the detection is based on type-II interband transitions between the hole energy levels located in the GaSb layers and electron energy levels in the InAs layers. The flexibility of the closely lattice-matched material system of InAs, GaSb and AlSb allows for engineering of the band gap for tailoring of the detection wavelength within the medium-wavelength IR (MWIR, 3-5 m) region and the long-wavelength IR (LWIR, 8-14 m) region. This material system has also enabled new barrier based detector structures [1-4] which are designed to reduce the problems of small bandgap material detectors, such as tunneling across the band gap and dark current related to Shockley-Read-Hall (SRH) processes. One of these barrier designs, which has been developed in the IR photonics group at Jet Propulsion Laboratory, is the Complementary Barrier Infrared Detector (CBIRD). It consists of an InAs/GaSb absorber sandwiched between an InAs/AlSb hole barrier and an InAs/GaSb electron barrier. This detector is expected to have favorable electron transport properties with a lightly p-doped absorber enabling high minority carrier mobility [4]. One of the crucial objectives when developing high performance superlattice detectors is to monitor the material quality of the epitaxially grown detector material. The structural quality is determined by a combination of characterization techniques, such as X-ray diffraction (XRD), surface scanning and atomic force microscopy. The material quality and the optical properties are measured using photoluminescence (PL) and absorption spectroscopy, respectively [5, 6]. In the PL measurements excess electrons and holes are generated by incident laser radiation. These charge carriers relax to the SL band edges, and then they recombine, either radiatively, emitting the excess energy as PL or non-radiatively. The carriers that recombine non-radiatively are commonly trapped by deep centers or defect levels situated in the band gap [7]. A high PL intensity consequently indicates that the material has few non-radiative recombination paths caused by defects. However, the PL intensity is also influenced by other parameters, such as the doping concentration, the sample structure and sometimes by the thickness of the material if the recombination is influenced by surface recombination [7]. It is therefore important to evaluate samples with similar structures to enable a fair comparison of the material quality of different samples.