Carrier decay and luminescence characteristics in hadron irradiated MOCVD GaN

Abstract

Crystalline GaN is a promising material for producing of the radiation hard particle detectors of different types capable to operate in harsh areas of particle accelerators. Moreover, GaN crystals show rather efficient luminescence properties in several spectral bands under excitation by high energy radiation. Thereby, GaN material can be employed for fabrication of a combined device which is able to operate both as scintillating and charge collecting detector. However, the efficiency of such detectors and their functionality has insufficiently been investigated. This work is addressed to study the evolution of the efficiency of photon and hadron induced luminescence. To evaluate the density of excess carriers induced by the high energy protons, a correlation between the microwave probed photoconductivity transients and the proton induced luminescence intensity has been examined using 1.6 MeV protons to produce a nearly homogeneous and rather strong excitation in 2.6 μm thick MOCVD grown GaN epi-layers. To estimate the radiation hardness of such material, the evolution of the photoconductivity transients and of the proton induced photoluminescence characteristics has been studied by in situ measurements of the changes of luminescence intensity and photoconductivity decay rate during the exposure to a proton beam reaching fluences up to 1015 cm-2. The production rate of radiation defects, determined from in situ and post-irradiation examination of the changes of radiative and non-radiative recombination have been examined by combining penetrative hadron (nuclear reactor neutrons and 24 GeV/c protons) irradiations with those of the 1.6 MeV protons. The parameters of the efficiency κP of carrier pair generation by asingle proton of κP = nP/NP ≅ 1.3 × 107 cm-3 per proton and κPApr = 40 carrier pairs per a micrometer of layer depth per proton have been estimated. The production rate of radiation defects is estimated to be KP ≅ 0.6 cm-1 for both penetrative neutrons and for 24 GeV/c protons. The hadronirradiation determines both the creation of the specific radiation defects with rate of KP ≅ 0.6 cm-1 and the modification of the material structure by increasing its disorder. Increase of disorder has been deduced from the observed decrease of value of the stretched-exponent index.