Journal of Crystal Growth 81(1987) 483—488 483 North-Holland, Amsterdam DEVELOPMENTS AND TRENDS IN MBE OF Il-VI Hg-BASED COMPOUNDS Jean-Pierre FAURIE Department of Physics, University of Illinois at Chicago, P.O. Box 4348, Chicago. Illinois 60680, USA We report here some new developments in MBE of HgCdTe. We show that the crystallographic orientation of the CdTe substrate hasa strong influence on the Hg condensation coefficient. A (111)A face requires about one order of magnitude more mercury than a (111)B face when the growth occurs at 190°C, the (100) face falling in between. We confirm that GaAs is still the candidate for replacing CdTe as a substrate, n-Type doping using In as a donor has been successfully investigated. High mobilities and also high donor concentrations have been achieved, which is important for future device applications. Preliminary investigations show that despite the fact that the (100) orientation requires 4-5 times more mercury than the (111)B orientation, this orientation seems the most suitable in terms of growth control and electron mobilities. The study on the change in the Hg condensation coefficient between HgTe, HgCdTe and HgZnTe has confirmed that Cd weakens the Hg—Te bond whereas Zn is less harmful. 1. Introduction 2. Hg condensation coefficient — influence of the crystallographic orientation In five years [1] important progress has been achieved towards the growth by molecular beam Molecular beam epitaxial growth is difficult to epitaxy (MBE) of Hg 1 - ~Cd~Te epilayers. achieve for Hg1 - ~Cd~Te because evaporation of Since 1981, the crystal quality along with the this semiconducting alloy is highly non-congruent electrical performances of the epilayers grown by [4]. The mercury tends to evaporate preferentially MBE on CdTe (111)B orientation have been highly from the surface. As a consequence, it has been improved by raising the substrate temperature up experimentally shown that the condensation coef- to 200°C. In terms of crystal quality and electrical ficient for Hg is of the order of 10’ ~ for growth at performances, MBE layers can be compared with a substrate temperature of 190° C [2]. This previ- the best Hg1_~Cd~Te material grown by other ous determination of the Hg condensation coeffi- techniques. cient had been carried out for n-type The characteristics of the first photovoltaic de- Hg1 - dxCd~Te layers (with x close to 0.20) grown vice made on a p-type layer have been reported on CdTe (111)B substrates [2]. The condensation [2], demonstrating that Hg1~Cd5Te grown by coefficient for a given element is defined as the MBE is suitable for device application, ratio of the number of atoms incorporated in the The growth of high quality epitaxial single layers layer to the number of incident atoms impinging and heterostructures is of vital interest since this the surface. As we have pointed out before, a semiconducting alloy, which is already the most temperature range of 180—200°C is required to important for infrared technology, is now appear- grow high quality Hg1 ~Cd~Te films by MBE [5]. ing as a promising material for optical telecom- Therefore a very high Hg atom flux is necessary to munication systems [3]. maintain the epitaxial grown conditions and as a In this paper we shall present and discuss the consequence a high amount of mercury is new developments and trends in MBE of Il—VI evaporated in the growth chamber. To reduce the Hg-based compounds with special attention to Hg consumption it has been proposed to ionize HgCdTe. the Hg but a uniform low energy ion flux is 0022-0248/87/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)