Relaxation of electrical properties of n-type layers formed by ion milling in epitaxial HgCdTe doped with V-group acceptors

Abstract

The relaxation of electrical properties of As-and Sb-doped HgCdTe epitaxial layers, which were converted into n-type by ion milling, is studied. It is shown that donor complexes formed under ion milling and responsible for p-to-n conductivity type conversion are not stable, and their concentration decreases upon storage even at room temperature. Increasing the temperature of the storage speeds up the relaxation process. It is demonstrated that the relaxation is caused by the disintegration of the donor complexes that starts right after the end of the milling process because of the decrease in the concentration of interstitial mercury atoms, which were generated during the milling. The results presented in the paper are important for the development of the technology of photodetectors based on HgCdTe doped with V-group acceptors.

Electrical properties of HgCdTe films grown by MOCVD and doped with as

“…Interestingly, however, in samples 1 and 3 the electron mobility extracted with DMSA right after the milling appeared to be higher than that in the as−grown samples. This contrasts these films to other MCT samples studied earlier [10,11,16,19,20], and could be explained by partial de−compensation of the film occurring via Hg vacancy filling and formation of donor complexes comprising As atoms, as described below, along with the relatively low total concentration of donor complexes right after ion milling.…”

“…The defect structure of this layer is defined by the reactions between the defects in the sample and the interstitial mercury Hg I injected into the crystal from the milled surface. The Hg I atoms, first of all, fill the existing vacancies, but they also react with the acce− ptors belonging to I (Cu, Ag, Au) and V (As, Sb) groups [15,16]. As a result, the acceptor centres get transformed into the donor ones, which is the reason for the material always having n−type after the milling.…”

“…Also, relaxation data are shown for a nominally un−doped n−type MBE film grown on a GaAs substrate, and a vacancy−doped p−type MBE film grown on a Si substrate. Details on the fabrication of the ISOVPE and MBE films and on the study of their properties with the use of ion mill− ing were given elsewhere [10,11,16,19,20]. Straight after the milling the mobility of the electrons μ n was quite low for the given x values.…”

Background donor concentration in HgCdTe

“…We studied films grown with MOCVD on CdZnTe and CdTe−buffered semi−insulating (111)B GaAs substrates at VIGO System [28] and with MBE on (311) GaAs [29]. The relaxation of n 77 and μ n77 of two MBE and two MOCVD films with x »0.2 grown on GaAs substrate is shown in figure 8 along with the similar data for an isother− mal vapour phase epitaxy (ISOVPE, yet another vapour− −phase epitaxy method) arsenic−doped film grown on a CdTe substrate at Ivan Franko National University in Lviv, Ukraine [17]. Presuming low concentration of As Hg defects in arsenic−doped films, after the relaxation the electron con− centration should have been defined by BDC.…”

“…vapours), while under IM the electrical compensation was reduced in relation to both vacancies and acceptor impuri− ties. For the latter process, a certain value of the Hg i concen− tration is needed [17], which cannot be achieved in ion−im− planted samples due to the high density of radiation−induced defects that serve as traps for Hg i .…”