Fast Proton Damage Effects on the Luminescence Properties of High-Quality GaN
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Fast Proton Damage Effects on the Luminescence Properties of High-Quality GaN Qing Yang, Henning Feick*, Rob Armitage, and Eicke R. Weber Department of Materials Science and Engineering, Univ. of California, Berkeley, California 94720, USA ABSTRACT High-quality GaN layers grown by hydride-vapor phase epitaxy (HVPE) and homoepitaxial layers grown thereon by molecular beam epitaxy (MBE) are studied after fast proton irradiation. A radiation-induced decrease of the band edge luminescence is observed. Time-resolved photoluminescence (PL) reveals a significant reduction of the carrier lifetime. A lifetime degradation constant of Kτ = 4×10-15 cm2/ns is reported for very thick HVPE GaN, and large variations are observed for the different layers. Partial recovery of the carrier lifetime and PL intensity with annealing is observed for thin HVPE GaN but not for the MBE overgrowth layer. INTRODUCTION GaN-based devices are about to be introduced in space-based systems and other radiation environments, prompting for a systematic study of radiation effects in GaN materials and devices. It has been reported that proton irradiation quenches the room temperature optical output of AlGaN/InGaN/GaN light emitting diodes [1]. Moreover, the performance of AlGaN/GaN high electron mobility transistors (HEMTs) was found to degrade with proton irradiation [2, 3]. At the microscopic level, Hall effect measurement and deep-level transient spectroscopy (DLTS) have been successful in detecting radiation-induced trap signatures [4,5,6]. With regard to optical properties it was found that irradiation with electrons and protons causes quenching of the photoluminescence (PL) intensity and additional PL bands in the near-infrared [7,8]. Intrinsic defects like N-vacancy/N-interstitial Frenkel-pairs [4,5] and Ga interstitials [7] have been reported. However, the influence of defects in the as-grown material as well as the interaction with dopants has not been systematically investigated. In an effort to gain more insight in this field, we study different types of GaN layers grown by hydride-vapor phase epitaxy (HVPE) and by molecular beam epitaxy (MBE). Our focus is on the optical emission (luminescence) properties. To the best of our knowledge, we report for the first time the effect of proton irradiation on the lifetime in GaN. EXPERIMENTAL DETAILS Three wurtzite GaN samples were chosen for this study. A free-standing 160 µm thick GaN layer grown by HVPE, a 10 µm HVPE GaN layer on sapphire, and a Si-doped homoepitaxial layer grown thereon by MBE using our Riber 1000 system. Irradiations were carried out at room temperature using 25 MeV and 55 MeV protons from Lawrence Berkeley National Laboratory’s 88 Inch Cyclotron. While the free-standing HVPE GaN layer was irradiated with a range of fluences (Φp = 2.7×1012…2.7×1014 cm-2) both the 10 µm HVPE GaN on sapphire and the MBE GaN layer were irradiated simultaneously with Φp = 8.5×1014 cm-2. 15-min isochronal annealings up to 600°C were carried out in air. *
on leave from center of advanced european studi
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