P+-InAsSbP/ n -InAs photodiodes for IR optoelectronic sensors

Abstract

ABSTRACT The performance of p + -InAsSbP/ n-InAs infrared (IR) photodiodes prepared by liquid phase epitaxy technique (LPE) is investigated. The current-voltage and capacitance-voltage characteristics, photoresponse and noise spectra are investigated in the temperature range 77-300 K. The trap-assisted current is calculated and compared with experimental data. It is found that at near-room temperatures and small reverse biases U 0.2 V experimental I-U characteristics are determined by diffusion and generation-recombination mechanisms. The trap-assisted tunnelling is shown to be dominant at higher reverse biases. The heterojunction photodiodes have superior photoresponse spectra in comparison with homojunction photodiodes and high threshold para meters. Keywords : infrared, photodiode, InAs, liquid phase epitaxy, liquid phase epitaxy 1. INTRODUCTION Mid-wavelength IR photodetectors, light-emitting diodes (LED) and lasers based on binary InAs and ternary InAsSb compounds are regarded as the most important constituents of the next generation optoelectronic sensors for monitoring of atmospheric pollutants. Many of gaseous pollutants are known to have absorption lines in the mid-wavelength region between 2 and 5 µ m. For example, methane has strong absorption line at 3.3 µ m and two order of magnitude lower overtone at 1.65 µ m. Modern gaseous sensors ought to determine not only the total concentration of pollutants, but also their molecular species. The mid-wavelength IR photodetectors operated at room temperature are preferred solution from both practical and economic considerations. As to photodetectors on mid-wavelength IR spectral region, it can be covered by several types of commercially available devices made of II-VI, IV-VI and III-V semiconductors. Photodetectors made of HgCdTe ternary compounds can have potentially the best performance [1]. However, these materials have serious technological problems, which stem from their poor chemical and lattice stability, growth difficulties, surface passivation, etc . PbS and PbSe photoconductors have high detectivity at room and near-room temperatures. Their manufacture technology is matured and rather chip. At the same time, several important drawbacks can limit their usage in modern IR devices. Made of thin polycrystalline films these detectors exhibit significant 1/f noise up to frequencies of the order of 10