INTRODUCTIONIt has recently been demonstrated that the performance of mid-wave infrared (MWIR) HgCdTe photovoltaic detectors grown on silicon substrates 1-3 can be comparable to that of devices deposited on conventional CdZnTe substrates, despite a 19% lattice mismatch between the heteroepitaxial HgCdTe and the silicon. The maturity of silicon technology offers many potential advantages, including lower cost, larger array sizes, and highly developed processing capabilities. In the present work, we investigate the negative electroluminescence (NL) properties of HgCdTe photodiodes grown on silicon substrates and compare them to the results of a previous investigation of devices grown on CdZnTe substrates. 4 Negative luminescence is a nonequilibrium phenomenon that has been observed in reverse-biased photodiodes. A diode in thermal equilibrium with its surroundings absorbs above-gap radiation, creating an electron-hole pair, at a rate balanced by radiative electron-hole recombination. The blackbody luminescent power (P bb ) resulting from this radiative optical emission is proportional to the product of the equilibrium electron (n 0 ) and hole (p 0 ) concentrations, i.e., P bb ∼ n 0 p 0 . However, biasing the device sets up a steady-state nonequilibrium condition, which tips the balance between absorption and emission. In particular, a reverse bias can sweep out carriers before they have a chance to recombine radiatively (np < n 0 p 0 ), thereby reducing the emission. This NL phenomenon has been investigated for several decades, 5 although early structures were small and inefficient. Recent work has demonstrated that NL devices may provide a viable option in such applications as the cold shielding of cooled and uncooled focal plane arrays (FPAs), multiple-point nonuniformity corrections for FPA dynamic references, sources for IR spectroscopy, and IR scene projection. 6,7 Negative luminescence has been observed in a number of IR detector and light-emitting diode (LED) materials in the spectral region beyond 4 m, including InSb, 5,8 InSb/InAlSb heterostructures, 9 InAsSb, 10,11 InAs/InAsSb superlattices, 12,13 type-II InAs/GaSb superlattices, 14 and HgCdTe. 4,[15][16][17] The NRL previously characterized HgCdTe photodiodes ( co = 4.2 m) supplied by BAE Systems (formerly known as Sanders IR Imaging Systems, Lexington,We have investigated the negative luminescence properties of a midwaveinfrared (MWIR) HgCdTe photodiode ( co = 5.3 m at 295 K) grown on a silicon substrate. The internal negative luminescence efficiencies measured using a self-referencing optical technique were 88% throughout the 3-5 m spectral region and nearly independent of temperature in the 240-300 K range. This corresponds to an apparent temperature reduction of 53 K at room temperature and 35 K at 240 K. Efficiencies measured by an electrical modulation technique were consistent with the measured internal efficiencies and the measured reflectivity of the device. This is the highest efficiency and largest apparent reduction in temperature reported to...