CMOS-Compatible PureGaB Ge-on-Si APD Pixel Arrays
Pure gallium and pure boron (PureGaB) Ge-on-Si photodiodes were fabricated in a CMOS compatible process and operated in linear and avalanche mode. Three different pixel geometries with very different area-to-perimeter ratios were investigated in linear arrays of 300 pixels with each a size of 26 x 26 mu m(2). The processing of anode contacts at the anode perimeters leaving oxide covered PureGaB-only light-entrance windows, created perimeter defects that increased the vertical Ge volume but did not deteriorate the diode ideality. The dark current at 1 V reverse bias was below 35 mu A/cm(2) at room temperature and below the measurement limit of 2.5 x 10(-2) mu A/cm(2) at 77 K. Spread in dark current levels and optical gain, that reached the range of 10(6) at 77 K, was lowest for the devices with largest perimeter. All device types were reliably operational in a wide temperature range from 77 K to room temperature. The spectral sensitivity of the detectors extended from visible to the telecom band with responsivities of 0.15 and 0.135 A/W at 850 and 940 nm, respectively.