Corrugated quantum well infrared photodetectors with polyimide planarization for detector array applications

Recently, we have demonstrated a new light coupling scheme for quantum well infrared photodetectors (QWIP). The new detector structure, referred to as corrugated QWIP (C-QWIP), is created by chemically etching linear V-grooves through the detector active region. In this structure, normal incident light is directed into the detector active region through total internal reflection, with which the optical absorption of the material is increased. However, the exposed active layers have to be insulated by a dielectric material before the top metal contact can be deposited for bonding purpose. In this paper, we describe a multilayer planarization scheme using a polyimide dielectric, which is developed specifically for this detector geometry, and report the resulting detector performance. The photoresponse of the detector with linear V-grooves pattern is found to be a factor of 1.6 larger than that of a regular edge coupled detector when they are normalized to the same dark current level. No wavelength or size dependence is observed using this coupling scheme, for detector sizes ranging from 50×50 μm² to 500×500 μm². With these two coupling characteristics, a C-QWIP behaves as a detector with normal incident absorption, a feature that will greatly improve the manufacturability of detector arrays and can be expected to lead to widespread applications of the QWIP technology