Interdigitated-finger metal-semiconductor-metal photodetectors (MSM-PDs) are widely used for high-speed optoelectronic applications. Recently, GaAs MSM-PDs have been utilized as optoelectronic mixers (OEMs) in an incoherent laser radar (LADAR) system. InGaAs MSM-PDs would allow LADAR operation at eye-safe wavelengths, mainly 1.55 μm. Unfortunately, the Schottky barrier height on InGaAs is quite low (~0.1-0.2eV) leading to high dark current and, hence, low signal-to-noise ratio. To reduce dark current, the Schottky barrier is typically “enhanced” by employing a high-band-gap lattice-matched Schottky enhancement layer (SEL). Detectors using SELs yield low dark current, high responsivity, and high bandwidths. In this paper we analyze the mixing effect in InAlAs Schottky-enhanced InGaAs-based MSM-PDs. We find that the measured frequency bandwidth of such a mixer is smaller than when used as a photodetector. Moreover, the mixing efficiency depends on the light modulation and mixed signal frequencies and decreases non-linearly with decrease in optical power. This is not observed in GaAs-based and non-Schottky-enhanced InGaAs MSM-PDs. We present a circuit model of the MSM-PD OEM to explain the experimental results.