Optical detection of nonradiative recombination centers in AlGaN quantum wells for deep UV region

Abstract

By superposing a chopped below‐gap excitation (BGE) light on a cw above‐gap excitation and observing the intensity change of photoluminescence (PL) due to the BGE, we clarified a distribution of nonradiative recombination (NRR) centers in AlGaN multi‐quantum well (MQW) structures for the wavelength region of deep ultraviolet (UV). The decrease in band‐edge PL peak intensity at 10 K exemplified the presence of a pair of NRR centers in AlGaN well layers whose transition energy corresponds to that of the BGE. The BGE power dependence of the normalized PL intensity showed a quenching saturation due to trap‐filling effect of electrons in one of the centers which were activated by the BGE. The BGE energy dependence of the normalized PL intensity revealed that the optical activation energy of the dominant NRR process via these trap states in the AlGaN MQW is around 1.17 eV. The purely optical scheme of detection enables us to obtain clues for identifying defect levels in DUV region and eliminating them during growth process without any preparation of electrodes. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Nonradiative centers in deep‐UV AlGaN‐based quantum wells revealed by two‐wavelength excited photoluminescence

“…As a purely optical scheme, it needs no electrode and has no limitation on sample size and geometry. In continuation to previous study on GaAs/AlGaAs, InGaN/GaN, InGaAs/GaAs, and other heterostructures , we have succeeded in detecting NRR centers in InAlGaN MQWs for DUV region. Possibilities of spectroscopic and quantitative detection and characterization of NRR centers were exemplified by determining a set of NRR parameters in a sample showing the PL intensity increase based on one level model.…”

Dominant nonradiative centers in InGaN single quantum well by time‐resolved and two‐wavelength excited photoluminescence

“…Finally, the PL intensity increases due to its direct proportional relationship with the product of np . However, the opposite trend is observed for other layers which can be explained by two levels model , as shown in Fig. (b).…”

“…The modulated PL signal guided by an optical fiber is collected in a CCD array via a monochromator and then recorded by a computer. In case of an energy‐matched NRR center exists, the BGE brings up electronic population of the center, which shifts the competition ratio between radiative and nonradiative recombination, then finally changes the PL intensity . The normalized PL intensity is defined as I N = I AGE+BGE / I AGE , where I AGE and I AGE+BGE are the PL intensity without and with the BGE, respectively.…”

Defect‐enabled electrical current leakage in ultraviolet light‐emitting diodes

“…Heteroepitaxial growth of AlGaN‐based UV emitters on sapphire substrates requires effort to realize epilayers with a low density of threading dislocations . Many defects formed as a result of the lattice mismatch between AlN, GaN, and sapphire are known to form below‐bandgap states, which act as non‐radiative recombination centers and reduce internal quantum efficiency . Furthermore, it has been shown that threading dislocations can function as electrical current leakage paths .…”