Characterization of polishing induced defects and hydrofluoric acid passivation effect in ZnO

Abstract

We used depth-resolved cathodoluminescence spectroscopy and transient photovoltage spectroscopy (T-SPS) measurements to study the spatial distributions and densities of native point defects in bulk ZnO samples subjected to mechanical polishing and how the defects change with hydrofluoric acid (HF) etching. Mechanical polishing produces Zn vacancy-related defects that deplete free carriers at depths extending to 300-500 nm, while HF etching removes/passivates these defects as well as bulk oxygen vacancy-related defects, restoring the charge carriers below the etched surface. T-SPS defect density changes with polishing/etching correlate closely with deep level transient spectroscopy densities, demonstrating the applicability of T-SPS as a non-contact quantitative defect density measurement technique. V

Impact of Mg content on native point defects in MgxZn1−xO (0 ≤ x ≤ 0.56)

“…Trap state densities measured by t-SPS correlate with DRCLS intensities and display relatively good agreement 40 with Gür et al DLOS results, 30 as expected from previous DLOS/t-SPS comparisons. 41,42 Total DLOS deep level concentrations for x = 0%, 31%, 44%, 52%, and 56% of 50.6, 6.1, 6.8, 7.8, and 5.4 × 10 16 cm −3 , respectively, 30 also correlate with Figure 4(a). The bulk I(V C )/I(NBE) values for ZnO are consistent with positron annihilation spectroscopy (PAS) calibration values corresponding to ∼0.08 × 10 17 cm −3 in the bulk and 0.25 × 10 17 cm −3 at the surface.…”

Neutron irradiation effects on gallium nitride-based Schottky diodes

“…Neutrons add GaN deep level defects to those already present at different densities and rates measurable by T-SPS. 34 Figures 4(a) and 4(b) illustrate SPS spectra before and after fast (fast neutron fluence ¼ 1 Â 10 16 n/cm 2 ) and fast þ thermal neutrons (fast neutron fluence ¼ 1.2 Â 10 16 n/cm 2 , thermal neutron fluence ¼ 2.8 Â 10 16 n/cm 2 ). For n-type material, the population (de-population) of deep level defect levels with electrons will increase (decrease) n-type band bending, moving Fermi level E F lower (higher) relative to vacuum level E VAC and inducing contact potential differences CPD that begin to decrease (increase) at threshold energies indicative of defect level positions E T relative to the band edges.…”

“…for Boltzmann constant k B , temperature T, dielectric constant , free space permittivity 0 , bulk doping density N B . The factor of 40 is the normalization factor of 1=k B T. CPD slope change _ V 0 S when light turns on, CPD slope change _ V 1 S when light turns off, surface potential CPD V 0 S without light in dimensionless units (normalized to kT/q), saturated and normalized CPD V 1 S with light on, and 34,36,37 Figures 5(a) and 5(b) display surface densities obtained from T-SPS versus fast and fast þ thermal neutron fluences, respectively. The highest density defects in Fig.…”

“…5(a) using the surface depletion width W since photogenerated free carriers require an electric field in order to drift and change surface potentials. 34 From Poisson's equation 162106-3…”

Native point defect energies, densities, and electrostatic repulsion across (Mg,Zn)O alloys

“…A linear variation of Mg x Zn 1Àx O band gap is evident with Mg content up to 52% from both DRCLS and SPS. SPS work function changes at photopopulation and depopulation thresholds provided defect level positions with respect to band edges [10,11]. V O (V C ) energy level movements versus Mg% parallel valence (conduction) band edge variations, respectively, consistent with their orbital-derived nature.…”