MILLIWATT OUTPUT LEVELS AND SUPERQUADRATIC BIAS DEPENDENCE IN A LOW-TEMPERATURE-GROWN GAAS PHOTOMIXER

A cw output power up to 0.8 mW is obtained from a low-temperature-grow n (LTG) GaAs, 0.3 mum gap, interdigitated-electrode photomixer operati ng at room temperature and pumped by two modes of a Ti:Al2O3 laser sep arated in frequency by 0.2 GHz. The output power and associated optica l-to-electrical conversion efficiency of 1% represent more than a sixf old increase over previous LTG-GaAs photomixer results obtained at roo m temperature. A separate LTG-GaAs photomixer having 0.6 am gaps gener ated up to 0.1 mW at room temperature and up to 4 mW at 77 K. Low-temp erature operation is beneficial because it reduces the possibility of thermal burnout and it accentuates a nearly quartic dependence of outp ut power on bias voltage at high bias. The quartic dependence is expla ined by space-charge effects which result from the application of a ve ry high electric field in the presence of recombination-limited transp ort. These conditions yield a photocurrent-voltage characteristic that is very similar in form to the well-known Mott-Gurney square-law curr ent in trap-free solids.