Milliwatt output levels and superquadratic bias dependence in a low-temperature-grown GaAs photomixer

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Abstract
A cw output power up to 0.8 mW is obtained from a low‐temperature‐grown (LTG) GaAs, 0.3 μm gap, interdigitated‐electrode photomixer operating at room temperature and pumped by two modes of a Ti:Al2O3 laser separated in frequency by 0.2 GHz. The output power and associated optical‐to‐electrical conversion efficiency of 1% represent more than a sixfold increase over previous LTG‐GaAs photomixer results obtained at room temperature. A separate LTG‐GaAs photomixer having 0.6 μm gaps generated up to 0.1 mW at room temperature and up to 4 mW at 77 K. Low‐temperature operation is beneficial because it reduces the possibility of thermal burnout and it accentuates a nearly quartic dependence of output power on bias voltage at high bias. The quartic dependence is explained by space‐charge effects which result from the application of a very high electric field in the presence of recombination‐limited transport. These conditions yield a photocurrent‐voltage characteristic that is very similar in form to the well‐known Mott–Gurney square‐law current in trap‐free solids.