Broadband Near Infrared Laser Detector.

The near-bandgap photoemission from III-V photocathodes with a bandgap less than the heterojunction barrier was shown to be due to thermally-assisted emission over the barrier rather than tunneling through it. The effects of a reduction in escape probability with stress in the active layer have been shown to be very important in the performance of transmission mode photocathodes, making thermal expansion matching considerations important. The problems involved in making ideal glass-sealed transmission photocathodes, including strain and Zn outdiffusion, are discussed and recently-improved performance is demonstrated. The necessity for treating four element-grown heterojunctions as graded quaternaries is demonstrated and applied to transmission photocathodes. Record-setting quantum efficiencies are demonstrated from a quaternary active layer. Use of quaternaries introduces an additional degree of freedom, allowing independent choice of the transmission photocathode long and short wavelength cut-offs while maintaining the lattice matching condition.