Photoionization spectroscopy of deep defects responsible for current collapse in nitride-based field effect transistors

Abstract

This review is concerned with the characterization and identification of the deep centres that cause current collapse in nitride-based field effect transistors. Photoionization spectroscopy is an optical technique that has been developed to probe the characteristics of these defects. Measured spectral dependences provide information on trap depth, lattice coupling and on the location of the defects in the device structure. The spectrum of an individual trap may also be regarded as a 'fingerprint' of the defect, allowing the trap to be followed in response to the variation of external parameters. The basis for these measurements is derived through a modelling procedure that accounts quantitatively for the light-induced drain current increase in the collapsed device. Applying the model to fit the measured variation of drain current increase with light illumination provides an estimate of the concentrations and photoionization cross-sections of the deep defects. The results of photoionization studies of GaN metal-semiconductor field effect transistors and AlGaN/GaN high electron mobility transistors (HEMTs) grown by metal-organic chemical vapour deposition (MOCVD) are presented and the conclusions regarding the nature of the deep traps responsible are discussed. Finally, recent photoionization studies of current collapse induced by short-term (several hours) bias stress in AlGaN/GaN HEMTs are described and analysed for devices grown by both MOCVD and molecular beam epitaxy. Contents

Прыжковая проводимость и диэлектрическая релаксация в барьерах Шоттки на основе GaN

“…Резкое увеличение оптического поглощения в GaN вблизи оптических пороговых энергий hv th = 1.1−1.3, 2.1−2.5, 3.1−3.2 эВ наблюдалось ранее в ряде ра-бот [18][19][20][21]. В работе [18] показано, что оптическое поглощение увеличивается с энергией фотона hv как exp(hv/E 0 ), с параметром E 0 , изменяющимся в области от 1.5 до 3 эВ от 180 до 280 мэВ и равным 50 мэВ в урбаховских хвостах плотности состояний в обла-сти ∼ 3.10−3.42 эВ.…”

Trap detection in electrically stressed AlGaN/GaN HEMTs using optical pumping

“…These defects are in some cases, electrically active and contribute to carrier trapping that adversely affects the device's performance. The role that traps play in nitridebased FETs is well documented [26][27][28][29][30][31][32][33][34][35].…”

“…Photoionization techniques have been used to identify traps in AlGaN/GaN HEMTs [27]. Illuminating a device with light energy greater than the energy of a trap releases a carrier from a defect, leading to de-trapping and increasing the drain current.…”

Photoionization of trapped carriers in avalanche photodiodes to reduce afterpulsing during Geiger-mode photon counting

“…In this paper, we introduce a method to reduce afterpulsing at any operating temperature, namely, photoionization of the trapped carriers with sub-band-gap energy illumination. Our method borrows from the optical technique of photoionization spectroscopy [6], where sub-band-gap light is used to probe, identify and quantify trapping levels (most notably in nitride-based field-effect transistors). Our method for reducing the afterpulsing effect (Fig.…”