Large improvement in HgCdTe photovoltaic detector performances at LETI

Abstract

The standard infrared photovoltaic technology developed for HgCdTe by LETI and industrialized by SOFRADIR is based on the very simple approach of planar ion-implanted n-on-p homojunctions. Both the growth by liquid-phase epitaxy of excellent-quality epitaxial layers and the simplicity of the planar ion-implanted process enables state-of-the-art detectors to be achieved with a high technological yield. These detectors present high shunt impedance, good quantum efficiency, and a low l/f noise level. The diodes are diffusion-limited down to temperatures much lower than 77K. Their saturation current is limited by the minority-carrier lifetime in the p-side material. R₀A values around 30 ohm-cm² are routinely obtained for 10.0 μm cutoff wavelength detectors at 77K. In this paper, we show that with a new process we can increase the diode R₀A by more than one order of magnitude. This effect is obtained as a result of an increase of minority-carrier lifetime in the n-on-p homojunction configuration. The maximum R₀A value obtained was 655 ohm-cm² on a 10.0 μm cutoff wavelength detector at 77K. Furthermore, other figures of merit much as quantum efficiency or shunt impedance are slightly improved, and l/f noise is not affected. The data presented in the 40–200K temperature range and 9–13 μm cutoff wavelength range show that this decrease of dark current is kept throughout these temperature wavelength ranges. Therefore, we show that a simple planar ion-implanted homojunction can lead to very large R₀A, close to theoretical limits and comparable to data published for p-on-n heterojunctions.