Capture kinetics at deep‐level electron traps in GaN‐based laser diode

Abstract

Two deep-level electron traps, E1 at E C − 0.23 eV and E2 at E C − 0.55 eV, have been revealed by means of deep-level transient spectroscopy (DLTS) in a GaN-based laser-diode heterostructure grown by metalorganic vapour-phase epitaxy on a bulk GaN substrate. The two traps represent different electron capture behaviours. The E1 trap, which exhibits the logarithmic capture kinetics and the DLTS-line shape characteristic of band-like electron states, is attributed to the core states of threading dislocations in a p-type layer of the structure. In contrast, the E2 trap, being the most prominent deep-level electron trap in GaN layers, displays the exponential capture kinetics and is assigned to isolated point defects, likely the nitrogen antisite defect.1 Introduction GaN-based III-V nitrides (GaN, InGaN and AlGaN) are wide direct band-gap semiconductors, which have already been applied successfully to optoelectronic devices, such as highbrightness blue light emitting diodes and lasers and solar-blind ultraviolet detectors [1]. Because of low thermal generation of charge carriers and large dielectric breakdown fields of these materials they have also found applications in high-temperature and high-power electronics [2]. However, owing to the large dislocation densities in the GaN epitaxial layers, commonly grown on highly-mismatched sapphire substrates, and self-compensation tendencies of wide band-gap semiconductors, a number of deep-level defects, affecting the performance and reliability of GaN-based devices, are usually present in the layers. Identification and understanding of these defects, especially dislocations, is of particular importance for improving the device technology.Deep-level transient spectroscopy (DLTS) is commonly used from already three decades as a powerful experimental technique for investigations of deep-level defects in semiconductor materials and structures. It allows characterizing and cataloguing deep levels by means of their capture cross-section and activation energy of thermal emission of charge carriers form the levels [3]. Additional information on the structure of deep-level defects can be gained while measuring the kinetics for capture of charge carriers into the defect states by means of recording the dependence of the DLTS-signal amplitude on the filling-pulse duration. In this respect, deep levels associated with extended defects, such as dislocations, distinctly differ from deep levels associated with isolated point defects or impurities, which exhibit exponential capture kinetics. On the contrary, deep levels related to dislocations are distinguished by logarithmic capture kinetics [4,5]. Such a kinetics results from the formation of a Coulombic barrier around the charged dislocations whose height increases with the filling-pulse duration [6].

Deep-Level Defects in MBE-Grown GaN-Based Laser Structure

“…More recent results by Chung et al [14] and Cho et al [10], showing that the concentration of this trap could be effectively suppressed by In doping, support this assignment. Very recently, this trap has been also revealed as the dominant deep-level defect in MOVPE-grown LD heterostructure [11]. However, in our present results the T2 trap concentration is the smallest of all deep-level traps recorded in the DLT spectra.…”

“…The appearance of dislocations in the LD heterostructure grown on the lattice-matched GaN substrate with a very low dislocation density may arise due to the growth of lattice-mismatched AlGaN and InGaN layers, which can give rise to dislocation generation during strain relaxation. Likely the same trap, called E1, was recently revealed in the DLT spectra measured in n-type GaN layers grown by metal-organic vapour-phase epitaxy (MOVPE) on sapphire [9,10] and in MOVPE-grown LD heterostructure [11], and attributed to the core states of threading dislocations.…”

“…Only one of these traps, the T2 trap, has been reported in the literature. This trap, with the activation energy at E C − 0.50 ÷ 0.62 eV and labelled B2, D2, or E2 in the literature, tends to be the most prominent electron trap revealed by DLTS in n-type GaN [10][11][12][13][14][15]. Hacke et al [12] and Haase et al [13] assigned this trap to the nitrogen antisite point defect, N Ga , on the ground of the results of tight-binding calculations determining the deep donor level of N Ga at E C − 0.54 eV [16].…”

Trapping mechanisms in GaN‐based MIS‐HEMTs grown on silicon substrate

“…In this experiment, the substrate potential ( V B ) was set to 0 V. Figures a and b depicts the time‐resolved stress/recovery transients acquired applying an OFF‐state stress bias at ( V G ; V DS ; V B ) = (−8 V; 25 V; 0 V). Both stress and recovery kinetics rely on single exponential law, thus suggesting the involvement of bulk point‐defects . Thanks to OTF characterization, it can be noticed that not only the rate (i.e., the inverse of the fitting exponential time constant) of the R ON recovery, but also the rate of the R ON increase is thermally activated.…”

Analysis of Current Transport Mechanism in AP-MOVPE Grown GaAsN p-i-n Solar Cell

“…The sign of each peak indicates whether the observed defect acts as a trap for minority or majority carriers, while the measured capacitance is proportional to defect concentration. DLTS-based methods are very efficient in defect determination in different semiconductor materials and devices, such as diodes [85,86], Schottky diodes [68,69] and rectifiers [87,88], solar cells [5,89,90], bipolar [91] and HEMT transistors [92] or laser structures [93,94]. A digital modification of DLTS, the deep level transient Fourier spectroscopy (DLTSFS) method measures the complete capacitance transient as a C(t) array and transfers the data into a computer system.…”