RESONANT CAVITY-ENHANCED INGAAS-ALGAAS HETEROJUNCTION PHOTOTRANSISTORS WITH AN OPTICAL DESIGN FOR HIGH UNIFORMITY AND YIELD

We present uniformity data on resonant cavity-enhanced InGaAs-AlGaAs h eterojunction phototransistors (HPT's) with an optical design that pro motes high uniformity and yield, The HPT's operate in the wavelength r egion where the GaAs substrate is transparent and the data show the HP T's to be suitable for vertical integration with optical emitters or m odulators to form two-dimensional arrays of smart pixels operating in transmission mode. The absorbing region of the HPT consists of an InGa As multiple-quantum-well structure where the quantum wells (QW's) have been distributed to make the total absorption in the cavity insensiti ve to growth variations as well as the spatial matching of the standin g wave and absorbing QW's, Theoretically, we estimate the absorption t o be 39% +/- 1% of the incident optical power, even at wafer nonunifor mities of +/-2.5%. With these nonuniformities, the resonant wavelength moves +/-25 nm, making postgrowth tuning of the wavelength necessary, Experimentally, we show postgrowth tuning of the resonance wavelength without loss in uniformity. The arrays have good uniformity as well a s very high responsivities. The average responsivity is 160 A/W +/-15% from 927-955 nm, The standard deviation of a typical array is 0.5 nm in resonant wavelength and about 5% of the average responsivity, The d ifference between maximum and minimum values for an array is typically 3 nm in resonant wavelength and +/-10% of the average responsivity.