An Investigation of Long and Short Time-Constant Persistent Photoconductivity in Undoped GaN Grown By RF-Plasma Assisted Molecular Beam Epitaxy

Abstract

Photoconductance decay and spectral photoconductance measurements were made on a set of ten undoped layers of GaN grown by rf-plasma MBE. The layers, also characterized by Hall, photoluminescence and reflectance measurements, represented a wide variety in electrical and optical properties, and several were grown under atomic hydrogen. Spectral photoconductance indicated transitions at 1.0-1.1, 1.92, 2.15, 3.08 and 3.2-3.4 eV. All layers exhibited persistent photoconductivity to some degree. In contrast with previous reports, a clear correlation was not observed between persistent photoconductivity and yellow luminescence or, indeed, with any measurement made. Analysis of photoconductance decay indicates that more than one type of persistent photoconductivity may be present.

Persistent photoconductivity and optical quenching of photocurrent in GaN layers under dual excitation

“…No relationship has been evidenced by Beady et al, 15 Hirsch et al, 16 and Ptak et al. 31 According to other authors, 10,18,19 PPC and YL phenomena in GaN are related to each other via an intrinsic defect. Recently, Boglio et al 32 found a correlation between transient dynamics of the PC and yellow PL defects in GaN samples but no correlation was evidenced between the strength of yellow PL and the magnitude of the PPC effect.…”

“…18,19 At decay times higher than 1000 s, better fit is achieved with ␤ϭ0.37 that corresponds to the value found by Qiu and Pankove. 25 Note that two-time regimes of PPC in GaN were recently attributed 31 9,13,14 while in bulk GaN, the preference is given to vacancies 21,24,25,31,32 and/or antisite-type defects. 10,18,19,21,24 One model was invoked to explain the separation of carriers from traps by random local-potential fluctuations that reduce the recapture rate of the traps and give rise to PPC.…”

“…It was suggested recently that several electron transitions contribute to the yellow PL. 31 One of these transitions is related to the defect responsible for PPC, while the other ones are related to additional impurities or defects. The analysis of the photocurrent transients in Fig.…”

“…Nevertheless, the situation remains uncertain and rather confusing. Particularly, different schemes concerning the major role of electron 18,19,22 or hole [23][24][25]31,32 traps in these processes are currently under consideration. The microscopic nature of the defects responsible for the phenomena involved is also under discussion.…”

“…Hence, the DX centers as the origin of PPC and OQ effects in our samples are less probable. According to the previous reports, 10,18,19,24,25,31,32 Gallium vacancy (V Ga ) or nitrogen antisite (N Ga ) is proposed as possible a defect which gives rise to PPC and OQ effects in GaN layers. Usually, both effects are considered to arise from the same defect.…”