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 heterojunction phototransistors (HPT´s) with an optical design that promotes high uniformity and yield. The HPT´s operate in the wavelength region where the GaAs substrate is transparent and the data show the HPT´s to be suitable for vertical integration with optical emitters or modulators to form two-dimensional arrays of smart pixels operating in transmission mode. The absorbing region of the HPT consists of an InGaAs multiple-quantum-well structure where the quantum wells (QW´s) have been distributed to make the total absorption in the cavity insensitive to growth variations as well as the spatial matching of the standing wave and absorbing QW´s. Theoretically, we estimate the absorption to be 39%±1% of the incident optical power, even at wafer nonuniformities of 12.5%. 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 as 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 difference between maximum and minimum values for an array is typically 3 nm in resonant wavelength and ±10% of the average responsivity