Mercury cadmium telluride resonant-cavity-enhanced photoconductive infrared detectors

Abstract

Resonant-cavity-enhanced Hg1−xCdxTe photoconductive detectors for midwave infrared wavelengths are investigated for use in multi- and hyper-spectral sensor systems. Resonant-cavity-enhanced performance is modeled, and compared with measured performance of fabricated devices. The responsivity of fabricated devices shows resonant cavity enhancement, with performance limited by surface recombination.

Optical and Structural Properties of CdTe Grown by Molecular Beam Epitaxy at Low Temperature for Resonant-Cavity-Enhanced HgCdTe Detectors

“…9). By the end of Hg (1)x) Cd (x) Te layer growth, streaky RHEED indicates a twodimensional growth mode. As growth proceeds, however, the RHEED pattern indicates that the two-dimensional growth mode of CdTe degrades, becoming three dimensional.…”

“…First, the ÔCdTeÕ layers exhibit a composition of x % 0.95, because the Hg shutter is open during growth of this layer. Second, there are two interfaces between CdTe and Hg (1)x) Cd (x) Te layers: the CdTe on Hg (1)x) Cd (x) Te layer at approximately 625 nm depth and the Hg (1)x) Cd (x) Te on CdTe layer at approximately 325 nm depth. As growth proceeds from the substrate (at approximately 4,450 nm depth), CdTe and Hg (1)x) Cd (x) Te layers are grown alternatively (Fig.…”

“…Initial experimental results 1,2 indicate that the measured response of these mirrors differs from the model response, with the discrepancy indicating an error in the refractive index of the CdTe layer. The CdTe layers of these mirror stacks are grown at the same temperature as the Hg (1)x) Cd (x) Te layers, a temperature of~185°C, as opposed to~310°C preferred for CdTe growth by MBE. Growth of CdTe at the same temperature as HgCdTe is a means of limiting the out-diffusion of Hg from the stack during growth, to reduce the interdiffusion of Hg between the HgCdTe layers and the CdTe layers, and it allows for an uninterrupted growth.…”

“…1 The structure used for such detectors relies on a mirror stack grown by MBE consisting of alternating Hg (1)x) Cd (x) Te/CdTe layers. Initial experimental results 1,2 indicate that the measured response of these mirrors differs from the model response, with the discrepancy indicating an error in the refractive index of the CdTe layer. The CdTe layers of these mirror stacks are grown at the same temperature as the Hg (1)x) Cd (x) Te layers, a temperature of~185°C, as opposed to~310°C preferred for CdTe growth by MBE.…”

“…A mirror stack (designated Mirror Structure A) was grown with arithmetically varying layer thicknesses (Hg (0.6) Cd (0.4) Te varying between 180 nm and 250 nm, and CdTe varying between 200 nm and 320 nm), 2 while a full RCE detector (designated Mirror Structure B) employed the same mirror growth, with an added absorber layer (75 nm of Hg (0.7) Cd (0.3) Te) and a CdTe spacer of~1-lm thickness. 1 These samples were both grown with a substrate temperature of between 183°C and 185°C, using a Te 2 cell (between 320°C and 330°C) and one or two CdTe cells (with setpoints 475°C and 525°C), depending on the desired composition. The CdTe layers were grown with the Hg effusion cell open, resulting in some incorporation of Hg in the CdTe layers.…”