Dynamics of Anomalous Temperature-Induced Emission Shift in MOCVD-grown (Al, In)GaN Thin Films

Abstract

We present a comprehensive study of the optical characteristics of (Al, In)GaN epilayers measured by photoluminescence (PL), integrated PL intensity, and time-resolved PL spectroscopy. For not only InGaN, but also AlGaN epilayers with large Al content, we observed an anomalous PL temperature dependence: (i) an “S-shaped” PL peak energy shift (decrease-increase-decrease) and (ii) an “inverted S-shaped” full width at half maximum (FWHM) change (increase-decrease-increase) with increasing temperature. Based on time-resolved PL, the S shape (inverted S shape) of the PL peak position (FWHM) as a function of temperature, and the much smaller PL intensity decrease in the temperature range showing the anomalous emission behavior, we conclude that strong localization of carriers occurs in InGaN and even in AlGaN with rather high Al content. We observed that the following increase with increasing Al content in AlGaN epilayers: (i) a Stokes shift between the PL peak energy and the absorption edge, (ii) a redshift of the emission with decay time, (iii) the deviations of the PL peak energy, FWHM, and PL intensity from their typical temperature dependence, and (iv) the corresponding temperature range of the anomalous emission behavior. This indicates that the band-gap fluctuation responsible for these characteristics is due to energy tail states caused by non-random inhomogeneous alloy potential variations enhanced with increasing Al content.

Optical properties of GaNAs and GaInAsN quantum wells

“…Finally, all excitons become delocalized, the tail emission dies and the peak follows the normal bandgap temperature dependence. This behaviour is well known for nitrides such as InGaN [69][70][71][72] and AlGaN [72], and is often seen in dilute nitride emission [62,[73][74][75][76].…”

Anomalous excitation dependence of electroluminescence in InGaN∕GaN light-emitting diodes

“…Motivated by experimental studies on anomalous luminescence phenomena and the role of compositional nonstoichiometry in ͑Al, In, Ga͒N-based optoelectronic devices, many researchers have characterized the radiative and nonradiative transition processes that occur in the disorderlike active regions of these devices. [1][2][3][4][5] Appropriate models have been developed to determine the contribution made to the optical characteristics by the structure-related heteropotential fluctuation. In terms of the large Stokes shift observed between the absorption edge and the emission energy of multicomponent alloys, the temperature-dependent S-shaped variation of the spectral peak is attributed predominantly to carrier localization phenomena.…”