Introduction and annealing of primary defects in proton‐bombarded n‐GaN

Abstract

We report on in situ space charge spectroscopy measurements on low‐temperature 1.6thinmathspaceMeV proton‐bombarded n‐type gallium nitride thin film samples. The scope of this study was to investigate the introduction and annealing dynamics of radiation‐induced lattice damage. Using optical excitation allowed for the detection of electronic defect states in the entire GaN bandgap and to detect unstable primary defects that would have been invisible in thermal space charge spectroscopic measurements. The introduction of compensating acceptor‐like primary defects by the bombardment was observed and manifested as a decrease in the sample capacitance. After the bombardment the concentrations of deep‐levels and acceptor states were monitored by deep‐level transient spectroscopy and photo‐capacitance measurements while the temperature was increased. It was found that annealing and reactions of primary bombardment‐induced defects occurs even below room‐temperature which might account for the radiation‐hardness of GaN.

Observation of low-temperature annealing of a primary defect in gallium nitride

“…Optical fibres were used to pass the light from the monochromator into the vacuum chamber where it was focussed onto the sample. Details of the setup are published in [10,13].…”

“…From PCap measurements (photon energies 3.0 eV < hν < 3.55 eV) the acceptor concentration was obtained to 1.3 × 10 16 cm −3 . In the first experiment the procedure that we proposed in [10] was used: (1) Firstly, the as-grown sample was cooled to 20 K. (2) Then it was bombarded with 1.6 MeV-protons at a fluence of 10 14 cm −2 such that primary defects were introduced into the lattice. Thereby the low temperature ensured that the introduced defects were immobile and thus unable to anneal or react with each other.…”

“…Low-temperature annealing of electron irradiation-induced defects in the Ga-sublattice was observed by low-temperature optical detected electron paramagnetic resonance and photoluminescense studies [9]. The authors reported on annealing at temperatures as low as 60 K. In our previous work [10] we introduced lattice defects into GaN by low-temperature proton-bombardment of the sample. The characterisation of the defects, in particular their electronic states, was carried out in-situ by means of optical space charge spectroscopy [2,11].…”