The n-type homojunction triangular barrier photodiode (TBP) is shown to have an extremely high optical gain of several thousands. This high gain at low light levels is shown to result from the low thermal generation rate of holes in the active region of the TBP, indicating a small concentration of deep traps in the material. A detailed analysis of the dependence of responsivity on applied voltage bias, incident optical power level, and physical device parameters has been made. This analysis indicates that the bandwidth of the TBP can be increased by either increasing the applied bias or by significantly increasing the intensity of the incident light.