Infinite-melt vertical liquid-phase epitaxy of HgCdTe from Hg solution: Status and prospects

Abstract

Liquid-phase epitaxy (LPE) has emerged as the predominant materials growth technology for the fabrication of HgCdTe infrared (IR) detectors in the IR community over the past decade. This paper reviews the current status as well as the evolution of one modification of LPE technology, specifically, “infinite-melt” vertical LPE (VLPE) from Hg-rich solutions. The backside-illuminated hybrid focal plane array (HFPA) approach for IR detection has been established in the past few years as the most attractive one for both scanning and staring modes in either tactical or strategic applications. Photodiode structures used in HFPA's with state-of-the-art performance in the entire 2–12 μm spectral region, including p-on-n as well as n-on-p double-layer heterojunctions (DLHJs), have been prepared by VLPE. This is mainly due to two unique characteristics inherent in the Hg-rich solution: (1) Low liquidus temperature ( <450 °C), which makes feasible the cap-layer growth step required for the DLHJ structure (2) Ease of intentionally incorporating temperature-stable impurity dopants, such as As, Sb, and In, in the HgCdTe layers during growth. It has been generally recognized that the DLHJ is the key element to further improvement in photovoltaic (PV) HgCdTe detector performance for LWIR applications. Knowledge of fundamental material properties for the Hg-Cd-Te system is reviewed in three main areas: phase diagram, defect chemistry, and impurity doping. The review concludes with a discussion of the prospects for use of the VLPE technology for investigating fundamental material properties of HgCdTe as well as fabricating advanced device structures of high performance.