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An AlGaAs-GaAs-based resonant-cavity-enhanced, heterostructure metal-semiconductor-metal photodetector with delta modulation doping operating at 850 nm is reported. Delta doping of the top AlGaAs layer produces a confined electron cloud and an associated electric field. Photocurrent spectral response shows the delta-doped photodetector has larger spectral response than the undoped one at all wavelengths. The delta-doped device also shows lower dark current and higher photo response compared to an undoped one, resulting in over an order of magnitude increase in its dynamic range. Time responses indicate that the doped devices have larger amplitudes but smaller full-width at half-maximum (FWHM) than the undoped ones. The increase in responsivity and speed of response is attributed to the vertical electric field and suitable potential profile in the direction of growth, while the decrease of the dark current is due to the confined electron cloud.