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We analyze the optoelectronic mixing characteristics of an InAlAs, Schottky-enhanced, InGaAs-based metal-semiconductor-metal photodetector. We show that the mixing efficiency of this device depends on the thickness of the InAlAs Schottky-enhancement layer: For thick enhancement layers (≈ 500 Å), the bandwidth of the device when utilized as an optoelectronic mixer is less than the bandwidth of the device when utilized as a simple photodetector. In addition, the mixing efficiency depends on the light-modulation, local-oscillator, and mixed-signal frequencies, and decreases nonlinearly with decrease in optical power. For thin enhancement layers (≈ 100 Å), the mixing characteristics improve: The bandwidth of the optoelectronic mixer is similar to that of a corresponding photodetector and the mixing efficiency decreases only slightly with decrease in optical power. We attribute the observed behavior to the band-gap discontinuity associated with the InAlAs Schottky enhancement layer.