Fourier transform infrared (FTIR) spectrometer is a powerful tool for studying the photoluminescence (PL) properties of semiconductors, due to its well-known multiplexing and throughput advantages. However, it suffers from internal He–Ne laser disturbance in near-infrared and∕or environmental background thermal emission in mid- and far-infrared spectral regions. In this work, a modulated PL technique is developed based on step-scan (SS)-FTIR spectrometer. Theoretical analysis is conducted, and applications of the technique are given as examples in the PL study of mid-infrared HgCdTe thin films and near-infrared GaInP∕AlGaInP multiple quantum wells, respectively. The results indicate that the He–Ne laser and∕or thermal emission disturbance can be reduced at least 1∕1000 and∕or even 1∕10000, respectively, by the modulated SS-FTIR PL technique, and hence a rather smooth PL spectrum can be obtained even under room temperature for HgCdTe thin films. A brief comparison is given of this technique with previously...

Modulated photoluminescence spectroscopy with a step-scan Fourier transform infrared spectrometer

We report on a new technique of realizing photoreflectance (PR) spectroscopy with a step-scan Fourier-transform infrared spectrometer. The experimental configuration is briefly described and a detailed theoretical analysis is conducted. The results reveal two distinct features of this PR technique that (i) the PR related signal is enhanced by a factor of at least 100 relative to those of the conventional PR techniques and (ii) the unwanted spurious signal introduced by either diffuse reflected pump beam or pump-beam induced material's photoluminescence reaching the photodetector of the PR configuration is eliminated without any special consideration of normalization for deducing the final PR spectrum. Applications are given as examples in the study of GaNAs/GaAs single quantum wells and GaInP/AlGaInP multiple quantum wells, respectively, under different pump-beam excitation energy and/or power. The experimental results approve the theoretically predicted features and illustrate the possibility of investigating weak PR features by using high pump-beam power. A brief comparison of this technique with the conventional PR techniques is given, and the extendibility of this technique to long-wavelength spectral regions is pointed out.

Photoreflectance spectroscopy with a step-scan Fourier-transform infrared spectrometer: technique and applications.

Room-temperature InAs/InAs1−xSbx strained-layer superlattice light-emitting diodes (x∼8%) are reported that emit at λ∼4.2 μm with an internal efficiency of 2.8%. The structures are grown by molecular beam epitaxy on slightly mismatched InAs substrates and include a strained AlSb barrier layer to prevent electron migration to the dislocated substrate–epilayer interface region. Comparison with a near identical structure grown without the barrier layer indicates a factor of four improvement in device efficiency at room temperature.

Room-temperature InAsSb strained-layer superlattice light-emitting diodes at λ=4.2 μm with AlSb barriers for improved carrier confinement

Vertical uniformity of HgCdTe epilayer is a crucial parameter for infrared detector engineering. In this work, backside illuminated infrared photoluminescence (PL) and photoreflectance (PR) measurements are carried out on an arsenic-doped Hg1−xCdxTe layer molecular-beam epitaxially grown on GaAs substrate, and the alloy composition and impurity states of the HgCdTe near the substrate are evaluated. By comparing to frontside illuminated PL and PR data, the vertical nonuniformity of composition and impurity states are evidenced. The results indicate that backside illuminated PL and PR are good pathway for evaluating contactlessly the nonuniformity of alloy composition and impurity states along the growth direction.

Backside-illuminated infrared photoluminescence and photoreflectance: Probe of vertical nonuniformity of HgCdTe on GaAs

Infrared modulated photoluminescence (PL) spectra are recorded in the temperature range of 11.5-290 K for both as-grown and p-type annealed arsenic-doped narrow-gap HgCdTe epilayers prepared by molecular beam epitaxy. Curve fittings indicate that conduction band-to-valence band transition is just detectable at 77 K but will dominate the PL line shape at temperatures above about 200 K. Below 100 K, transitions are mainly impurity-related. Shallow impurity levels are estimated to be about 12, 20, 17, and 26 meV, respectively, for VHg and AsTe as acceptors, and AsHg and TeHg as donors, which are very similar to those established by theory and/or infrared photoreflectance spectroscopy. The p-type annealing removes deep level-related PL features that are only observed in the as-grown HgCdTe epilayer. Comparison with previous PL study suggests that infrared modulated PL technique can serve as an easily accessible pathway for characterizing impurities in narrow-gap HgCdTe when PL spectra are recorded with good signal-to-noise ratio in a wide range of up to room temperature.

Infrared photoluminescence of arsenic-doped HgCdTe in a wide temperature range of up to 290 K

Semiconductor materials commonly used in mid‐ and long‐wavelength infrared sensing applications generally have a low radiative efficiency, and the ambient blackbody radiation spectrum often dominates and interferes with the identification of the photoluminescence peak. Two techniques designed to facilitate the extraction of the spontaneous radiative spectrum are discussed and compared.

R. N. Roberts

Papers

Photoluminescence of infrared‐sensing materials using an FTIR spectrometer