2.3 Micrometer Sensitive, High Speed, Extended InGaAs Avalanche Photodiodes

In Phase I, Spire will epitaxially grow, fabricate, and test two types of avalanche photodiodes (APDs) using 0.55 eV (2.3 mm cutoff wavelength) indium gallium arsenide In0.72Ga0.28As. This material will be "extended" past the common 0.74 eV lattice-matched In0.53Ga0.47As by use of an InxGa1-xAs grading layer. One APD type will have both absorption and multiplication/junction regions in the 0.55 eV InGaAs. The second type is more complex but should have much less noise. This APD uses a separate 0.55 eV InGaAs absorption, InxGa1-xAs grading, and 1.34 eV InP multiplication/junction region should minimize the tunneling dark current which plagues low-bandgap APDs. Spire has sold thousands of 2.3 mm InGaAs photovoltaic devices in InxGa1-xAs grading layers on InP wafers for thermophotovoltaic power conversion which had high (>70%) quantum efficiency. This existing epitaxial growth and processing technology base will enable Spire to make working APD prototypes in Phase I. Phase II will concentrate on improving performance, creating arrays, and addressing packaging and marketing issues of the more promising of the two phase I APDs.