A symmetric gain optoelectronic mixer based on an indium gallium arsenide (In0 53Ga0 47As)/indium phosphide (InP) symmetric heterojunction phototransistor structure is being investigated for chirped-AM laser detection and ranging (LADAR) systems operating in the eye safe 1 55 mu m wavelength range Signal processing of a chirped-AM LADAR system is simplified if the photodetector in the receiver is used as an optoelectronic mixer (OEM) Adding gain to the OEM allows the following transimpedance amplifiers gain to be reduced increasing bandwidth and improving the system s noise performance A symmetric gain optoelectronic mixer based on a symmetric phototransistor structure using an indium gallium arsenide narrow bandgap base and indium phosphide emitter/collector layers is proposed The devices are simulated with the Synopsis TCAD Sentaurus tools The effects of base-emitter interface layers base thickness and the doping densities of the base and emitters on the device performance are investigated AC and DC simulation results are compared with a device model Improved responsivity and lower dark current are predicted for the optimized InGaAs/InP device over previously reported devices with indium aluminum arsenide emitter/collector layers (C) 2010 Elsevier Ltd All rights reserved