Structural characterization of H plasma‐doped ZnO single crystals by Hall measurements and photoluminescence studies

Abstract

Nominally undoped, hydrothermally grown ZnO single crystals have been investigated prior to and after doping in remote H plasma. Characterizations have been made by temperaturedependent Hall effect (TDH) and low temperature photoluminescence measurements. The H content before and after the doping has been determined using nuclear reaction analysis and is compared to the density of shallow donors derived from the TDH measurements. The electrical properties of the asgrown ZnO single crystals are found to differ significantly. This is ascribed to the density ratio of shallow donors and compensating acceptors. PL measurements showed that Al Zn , Ga Zn , and interstitial zinc (Zn i ) are prominent shallow donors in the as-grown samples. Remote H plasma treatment produced a metallic conducting near-surface layer thus masking the electrical properties of the bulk. The electrical properties of the investigated samples are very similar after the treatment, independent of the as-grown state, because the density of shallow donors far exceeds that of compensating acceptors in the affected near-surface region. The maximum of the broad near-bandedge emission is found to be located at 3.3595 eV due to the high doping density.

Structural characterization of H plasma‐doped ZnO single crystals by positron annihilation spectroscopies

“…The presence of Zn i in the virgin crystal is reliably concluded from PL and Hall measurements – these results are reported and discussed in the second part of this paper 45. Unfortunately, no estimate concerning the Zn i concentration can be derived from these measurements.…”

“…1. The “as‐grown” material exhibits a single LT (182.2 ± 0.7 ps) 45 which should be indicative of saturation trapping in V Zn + 1H defects 1; however, a box‐shaped profile obtained by H + implantation with various fluences in the energy range (20–80) keV to achieve a total fluence of 4.4 × 10 15 cm −2 is also characterized by a single but slightly larger LT (202.0 ± 0.6 ps) 44 which strongly suggests saturation trapping in V Zn 1. Post‐implantation annealing at 700 °C is found to result in the formation of large empty microvoids which are interpreted as agglomerated V O defects.…”

“…In a second part of this work, complementary temperature‐dependent Hall (TDH) measurements for electrical characterization and supplementary PL studies have been performed on HTG ZnO single crystals, before and after treatment in remote H plasma, and an extensive discussion of the modification of electrical and optoelectronic properties is presented 45.…”

Characterization of H-Plasma Treated ZnO Crystals by Positron Annihilation and Atomic Force Microscopy

“…In the present work PAS studies were combined with characterization of H-plasma treatment-induced surface modifications by atomic force microscopy (AFM). This works is a continuation of previous investigations of H-plasma treated HTG ZnO single crystals by slow positron implantation spectroscopy (SPIS) combined with pulsed low energy positron spectroscopy (PLEPS) [6] and by Hall measurements combined with photoluminescence [7].…”

“…This could explain the observed decrease in the concentration of positron traps in a H-plasma treated ZnO crystal. The presence of Zn i in the virgin ZnO crystal is reliably concluded from photoluminescence and Hall measurements [7].…”