MOVPE growth and characterization of doped Cd_xHg_1-xTe structures

Abstract

This paper describes work carried o u t towards achieving extrinsically doped Cd,Hg, -,Te (CMT) heterostructures grown with stable dopants and sharp junctions. Both acceptor and donor doping of CMT has been achieved in our MOVPE growth reactor using the interdiffused multilayer process at -400 "C with diethyitellurium (DET) as the tellurium alkyl source. The two dopants used were arsenic, introduced as ASH,, and iodine, as vapour from the solid element. The donor doping range has been extended by t h e use of a concentrically arranged double-injection-tube system which reduced the pre-reaction between the cadmium alkyl and the iodine vapour. investigations have been carried out into the growth of various double-layer structures which incorporate either a single dopant transition or a double transition, as in a fully doped structure. concentrations and alloy compositions of As-doped ( x = 0.3) on undoped (x = 0.21) CMT heterostructures has shown that pn structures have been produced after suitable Hg anneal treatments. Iodine-doped x = 0.2 layers on As-doped x = 0.3 layers have also exhibited pn transitions. Results from fully doped homojunction layers grown with -1 x IO" I (atomic) cm --3 n-type regions on ( 1 4 ) x IO" atoms Ascm-" p-type regions have also been obtained which show sharp electrical junctions.Depth profiling to obtain the electrical characteristics, chemical dopant

Doping studies in MOVPE-grown CdxHg1-xTe

“…Characterization of the layers for electrical, chemical and compositional information involved Hall profiling scan ( t s ~s ) or secondary-ion mass spectrometry (SUMS) as described previously [7]. Uniess otherwise stated all the layers were given an open tube 200 "C isothermal Hg anneal for -65 h.…”

Morphological effects and the diffusion of iodine in CdTe

“…2a with the twin, apparently showing the higher defect density. The twin must have been present in the undiffused sample, but had not Figure 1 Micrographs showing tellurium precipitates in the surface of a CdTe slice that has been etched with Inoue's reagent [1] in (a) ( x 770) and a grain boundary associated with a much iarger single precipitate in (b) ( x 770)_ been noticed beforehand and could not have been caused by the diffusion anneal.…”

“…Requirements for finding a suitable donor for mercury cadmium telluride (MCT) and CdTe have led recent investigators to the halogens and in particular iodine, which has been shown to be a satisfactory n-type dopant in MCT [1]. As iodine is the largest of the group of elements J comprising the halogens, it was expected to be the least susceptible to diffusion [2].…”

Electrical activity of iodine-diffused CdTe

“…Investigations on the halogen doping of CdTe and Hg 1 − x Cd x Te (referred to as MCT) 1,2 have shown differences between the concentration profiles of the dopants measured using secondary ion mass spectrometry (SIMS) and capacitance -voltage (C-V) or Hall measurements. The former technique gives the total dopant concentration, whereas the latter give the concentration of electrically active species only.…”

“…The halogens have been used on a regular basis for some time as an n-type dopant in epitaxially grown devices, 2 but recent studies on the diffusion of iodine into CdTe from the vapour 3 have shown that complex diffusion profiles are produced which can be fitted satisfactorily by an empirical function composed of the sum of four complementary error functions. Four values of the diffusivities (D 1 -D 4 ) were obtained from each profile (see Fig.…”