AlGaAs/InGaAs PHEMT preamplifier for optical communication systems

The design, fabrication and characteristics of a AlGaAs/InGaAs PHEMT monolithic transimpedance preamplifier is described. The PHEMT material used here is based on δ-doped carrier supplying layer and GaAs/AlGaAs superlattice buffer. The transconductance and output conductance of a 1 μm-gate PHEMT is 250 mS/mm and 8mS/mm respectively with threshold voltage of -1.2 v, the maximum saturation current density is 235 mS/mm. On-wafer network analysis with HP8510 network analyzer shows its cut-off frequency of 21 GHz and maximum oscillation frequency of 40 GHz. Transimpedance preamplifier its measured maximum transimpedance gain of 51.4 dBΩ with -3 dB bandwidth no less than 5.05 GHz. The input equivalent-noise current density is 13 PA/√Hz