Metal-semiconductor-metal photodetectors for optoelectric receiver applications

Abstract

It has been found that the barrier height lowering observed in reverse-biased Schottky junction is due mainly to the change in electrical potential across the interfacial layer at the metal-semiconductor contact. The voltage dependence of barrier height is described, and excellent agreement with experimental data is shown. The surface state density and interfacial layer thickness of a (Ti/Au) /n-InAlAs Schottky junction are estimated from its I-V characteristics. The expressions of the barrier heights of junctions in a metal-semiconductor-metal photodiode (MSMPD) are derived, and excellent agreement with experiment is shown. The adjustment of barrier height and dark current by annealing is investigated based on the theory. The merit of transparent electrodes for MSMPD in an optoelectronic-integrated-circuit (OEIC) is described, and it is shown that the signal-to-noise-ratio (SNR) of a receiver can be improved by the employment of transparent electrodes.

The design, fabrication, and characterization of MSMPDs for long- $(\lambda = 1.3\ \mu$m) and short-wavelength $(\lambda = 0.85\ \mu$m) applications are presented in detail. The deposition by RF magnetron sputtering and etching by reactive-ion-etching (RIE) of ITO film are described. It has been found that H$\sb2$ incorporation in an Ar plasma during ITO deposition improves the optical transmittance of the film at $\lambda = 1.3\ \mu$m. Responsivity was doubled by ITO electrodes and an anti-reflection (AR) coating. Bandwidths (3-dB) of 22 GHz and 16.6 GHz were obtained for long- and short-wavelength MSMPD, respectively. A 3-dB bandwidth of 6 GHz was obtained for both long-and short-wavelength ITO-MSMPDs. It is shown that the wide band-gap barrier enhancement layer reduces optical responsivity by capturing carriers at the heterointerface. The effects of surface and surface passivation on MSMPD performance are studied. The characterization of OEIC receiver with a transimpedance amplifier is described.