On the character of defects in GaAs

Abstract

Positron lifetime measurements on GaAs are presented and discussed and former measurements are reviewed. The limitations and appropriate criteria for adequate spectrum analyses are considered in detail. It is shown that exceptionally good statistical accuracy is necessary for a reliable and consequential decomposition, and that source corrections are very important. Results for liquid phase electro-epitaxially grown GaAs conclusively show that the bulk lifetime for GaAs is 220+or-1 ps. All other GaAs samples (grown by either the liquid encapsulated Czochralski method or by the horizontal Bridgman method) show variable bulk lifetimes up to 232 ps. Shallow traps are concluded to be the cause for this. The binding energy of positrons in such traps is estimated to be about 23 meV, and the trapping rate into deep traps from such shallow traps is found to be approximately five times smaller than from the bulk state. The shallow trap is likely to be substitutional boron or nitrogen. The shallow traps anneal mainly around 700 K. Deep traps are found in all samples, yielding lifetimes tau DI approximately=260 ps and 290 ps<or= tau DII<or=315 ps. These lifetimes occur in n-type, p-type and semi-insulating materials. The results support the authors' earlier contention that the 290-315 ps components are due to divacancies and the 260 ps lifetime is due to monovacancies, in complex form with some impurity. The divacancy anneals around 620 K while the mono-vacancy-impurity complexes generally anneal around 800 K.

Semi-insulating GaAs: A possible substrate for a field-assisted positron moderator

“…This spectrum was subject to analysis with a four component fit, the first two components being fixed at the spectrum found for the GaAs using the intensity ratio constraint facility of POSI-TRONFIT. The remaining two components gave the [23] we associate the longer of the two components with annihilation in the NaCI, whereas the shorter of the two is similar to that observed by other workers [24] and may be attributed to defected Ni. Finally after the source and background corrections, it was found that all lifetime spectra were fitted well by the sum of two exponential components: …”

“…This spectrum was analyzed using POSI-TRONFIT [22] and found to be well represented by two lifetime components (404 ps at 3.5% and 223 ps at 96.5%). Following the work of Dannefear, et al on GaAs [23] with Field-assisted positron m o d e r a t o r varying levels of 22NaCI activity, we take this lifetime spectrum to be totally representative of the semi-insulating GaAs and not noticeably perturbed by annihilations in the NaC1. The lifetime spectrum was then taken for the same SI-GaAs samples (the 1.5 ~tCi source removed) using the 28 pCi Ni foil encapsulated source.…”

“…2 we found for non metalized samples of SI-GaAs 3.5% of a 404 ps lifetime. Dannefaer et al [23] performing similar studies on very pure Liquid-Phase Electro-Epitaxially (LPEE) grown GaAs find 5% of a 319 ps lifetime component. In both these cases, we believe it likely that some if not all of such long lived positron states are to be associated with the sample surfaces.…”

A search for defect configurational changes in the post‐breakdown metastability of semi‐insulating GaAs

“…Each lifetime spectrum contained 3 × 10 6 counts and was analyzed using the program of POSITRONFIT [8]. Due to the low activity of directly deposited source there was no need to carry out any source correction for annihilations in the micro-crystals of radioactive salt [9].…”

Defects Introduced by Low Dose Be-Implantation Probed by a Monoenergetic Positron Beam

“…Because of this unique character, the study of defects in compound semiconductors by positron annihilation techniques is a subject of increasing interest [3][4][5][6][7].…”