Positron annihilation spectroscopy for the determination of thickness and defect profile in thin semiconductor layers

Abstract

We present a method, based on positron annihilation spectroscopy, to obtain information on the defect depth profile of layers grown over high-quality substrates. We have applied the method to the case of ZnO layers grown on sapphire, but the method can be very easily generalized to other heterostructures ͑homostructures͒ where the positron mean diffusion length is small enough. Applying the method to the ratio of W and S parameters obtained from Doppler broadening measurements, W / S plots, it is possible to determine the thickness of the layer and the defect profile in the layer, when mainly one defect trapping positron is contributing to positron trapping at the measurement temperature. Indeed, the quality of such characterization is very important for potential technological applications of the layer.

On the interplay of point defects and Cd in non-polar ZnCdO films

“…The S and W parameters inside the buffer have been obtained from the experimental S and W parameters using a model of implantation and annihilation of slow positrons in semiconductor heterostructures with short positron diffusion length 16 to subtract the contribution from the ZnCdO film. The samples have been divided into three regions: the ZnCdO film, the ZnO buffer, and the sapphire substrate, and the annihilations parameters are assumed to be constant within each region.…”

“…). The thickness of the samples (film þ buffer) has been estimated as twice the mean implantation depth at the largest implantation energy before positrons start to annihilate in the substrate 16 (see Table I). The thickness of the ZnCdO film has been estimated subtracting the thickness of the buffer.…”

Effect of growth conditions on vacancy defects in MOVPE grown AlN thin layers

“…The thickness of the AlN layer has been estimated using method presented by Zubiaga et al in the paper [7]. The method gives estimated layer thickness 180-220 nm for all the samples, close to the nominal layer thickness given by the growth rate.…”

Vacancy defects probed with positron annihilation spectroscopy in In‐polar InN grown by plasma‐assisted molecular beam epitaxy: Effects of growth conditions

“…The decrease of the S parameter at higher implantation energies is due to the increasing fraction of positrons annihilating in the GaN template/buffer layer, for which the characteristic S parameter is roughly S = 0.46. It should be noted that the mean implantation depth above which the substrate starts to affect the data is roughly half of the layer thickness due to the rather wide positron implantation profile [11].…”