P-i-n photodiodes in metamorphic InAlAs-InGaAs-GaAs for long wavelength applications

InP-based heterostructures have traditionally been used for the fabrication of photodetectors and integrated optoelectronic circuits (OEICs) operating at long wavelength (1.55 /spl mu/m) for optical fiber applications. Specifically, In/sub 0.53/Ga/sub 0.47/As lattice-matched (LM) to InP is used for the absorption region in a photodetector and for the active channel in electronic devices. Recent advances in heteroepitaxy have resulted in the growth of high quality metamorphic (MM) In/sub 0.52/Al/sub 0.48/As-In/sub 0.53/Ga/sub 0.47/As layers on GaAs substrates using thick graded InAlGaAs buffer layers (Hoke et al, 1999). This push for metamorphic layers is being driven by the lower cost, robustness, and the mature processing technologies enjoyed by GaAs over InP. High performance high electron mobility transistors (HEMTs) with short gate lengths fabricated on GaAs MM layers have demonstrated record bandwidths (Dumka et al, 1999) similar to LM HEMTs on InP. In order to achieve lower cost, ultra-high speed (>20 Gb/s) OEICs, it is imperative to investigate the performance of optoelectronic devices such as p-i-n photodiodes in MM structures. In this paper, we report a comparative study of p-i-n photodiodes fabricated using metamorphic (MM-PIN) GaAs-based and lattice-matched (LM-PIN) InP-based heterostructures. Results on dark currents, DC, and RF responses are presented.