710 Journal of Crystal Growth 108 (1991) 710 718 North-Holland Isothermal vapor phase epitaxy of (Hg,Cd) Te from Te-rich Hg 1 ~Te~source Z. Djinovié, Z. Djurié, Z. Jak~ié,F. Kermendi and R. Roknié IHTM Institute of Microelectronic Technologies and Single Crystals, Njegoleva 12, Beograd 11000, Yugoslavia Received 12 April 1990; manuscript received in final form 18 October 1990 The method of isothermal vapor phase epitaxy (ISOVPE) of Hg1 ~Cd~Te layers with fixed surface composition is presented. The epitaxial growth was performed from a Te-rich Hg1 ~Te~ (y > 0.5) liquid source, in an open tube, two-temperature setup. The Hg partial pressure limits the surface composition of the layers. It is shown that the growth takes place under near-equilibrium conditions, except in the very beginning. Therefore, the time change of the surface composition and the composition gradient 3x dz is very low, especially near the surface. The dependence of the surface composition and the thickness of the layers on the main process parameters is considered, utilizing the general ISOVPE model. Very good agreement between the experimental and calculated values has been found. A comparison of composition profiles obtained by the epitaxial growth from solid and liquid sources is given. 1. Introduction lifetime significantly [4]. Secondly, the absorption length of incident radiation 1 — 1/cs (cm) for Eg Hg1 ~Cd~Teis the most important single crystal 0.1 eV (X peak 11 ~m) is severely reduced if the from the group of II VI compounds because it is layer composition gradient is sharper. It results in widely used for the production of infrared detec- a decrease of voltage responsivity of the device. It tors. It is a small-bandgap semiconductor with is necessary, therefore, to have as low a composi- energy gap varying from —0.30 eV (HgTe) to 1.65 tion gradient as possible, especially near the layer eV (CdTe) in dependence on composition and surface. temperature [1]. The obtaining of device quality The principal problem of ISOVPE is how to material by the standard growth methods is control the surface composition and gradient troublesome due to certain metallurgical proper- ax/Bz of the epitaxial layers. Vapor phase epitaxy ties of the HgTe CdTe system [2]. The epitaxial is usually performed in evacuated sealed quartz growth methods are thus becoming increasingly ampoules [5 7]. A few papers handle the growth important [3]. in open systems [8 10]. Various authors use dif- ISOVPE is a relatively simple method which ferent epitaxial growth sources. Most often it is enables simultaneous fabrication of several large HgTe on the border of three-phase equilibrium. area layers with excellent morphology and low Fleming and Stevenson [5] use Te-rich (Hg1 concentration of residual impurities to be carried Cd~ )~ ~ in equilibrium with the desired layer out. However, the composition gradient limits their composition. Here the molar fraction of Cd de- application to cooled photovoltaic (77 K) and termines the lowest surface x value of uncooled photoconductive (300 K) detectors. Un- Hg1 ~Cd~Te. Becla et al. [6] proposed composi- ill now, good photoconductors (77 K) have not tion control by mercury partial pressure in a two- been realized. There are at least two reasons for zone closed ampoule. that. The composition gradient generates many In this paper we consider the epitaxial growth misfit dislocations and thus decreases the carrier of Hg1 ~Cd~Te layers with a desired surface corn- 0022-0248/91/$03.50 ~E 1991 Elsevier Science Publishers B.V. (North-Holland)