unneling effects in InAs/GaInSb superlattice infrared photodiodes
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ABSTRACT The optical and electrical properties of InAs/GaInSb superlattice mesa photodiodes with a cutoff wavelength around 8 pim are investigated. The influence of the surface potential at the mesa sidewalls on the device properties was studied by fabricating gate-controlled diodes. At least two mechanisms determining the dark current in the reverse bias region can be identified. At high reverse biases bulk bandto-band tunneling dominates while the current at low reverse biases is most likely governed by surface effects. Bulk interband tunneling is further investigated by applying magnetic fields B up to 7 T parallel and perpendicular to the electric field E across the p-n junction. INTRODUCTION The InAs/GaInSb short-period superlattice (SPSL) system is suitable for long-wavelength detector applications due to the broken gap type II band alignment. An effective band gap between minibands in the superlattice can be opened due to quantization effects. After the first proposal as a possible alternative to HgCdTe in 1987 [1] the epitaxial growth has matured and the successful preparation of diodes has been reported by several groups [2-4]. The performance of a photodiode is generally limited by the dark current, which determines its dynamic impedance and its thermally generated noise. However, little work has been reported on dark current mechanisms in InAs/GaInSb SPSL photodiodes. It is known from other low gap materials that tunneling currents may dominate the current-voltage characteristic in reverse bias [5,6]. Tunneling may occur either across the metallurgical junction or across field induced junctions which are due to surface accumulation or inversion at the mesa sidewalls. Gate electrodes can be placed on the mesa sidewalls in order to control the surface potential and the surface leakage currents. Thus bulk properties may be distinguished from surface effects. DEVICE PREPARATION AND DETECTOR CHARACTERIZATION
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Fig. 1: (004) HRXRD rocking curves of a 100 periods 14 ML InAs/8 ML Gao.sIno. 2 Sb SPSL. The samples were grown by solid source MBE on undoped, but residual p-type, (100) GaSb at substrate temperatures around 410 0C. Alternating InSb-like and GaAs-like interfaces were employed, terminating each individual layer of the superlattice by a group V soak and starting the following layer by a monolayer (ML) of the respective group III material. This growth sequence was found to result in a superior quality in comparison to the inverted interface alternation [7,8]. Growth parameters such as substrate 123
Mat. Res. Soc. Symp. Proc. Vol. 484 (@1998Materials Research Society
temperature and III/V beam equivalent pressure ratios were optimized using Fourier-transform IR photoluminescence spectroscopy and high-resolution X-ray diffraction (HRXRD) yielding bandgap, average strain and superlattice period, respectively. Meanwhi
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