Photoluminescence features and carrier dynamics in InGaN heterostructures with wide staircase interlayers and differently shaped quantum wells

Abstract

We present a comprehensive study of photoexcited carrier dynamics in differently grown InGaN/InGaN multiple quantum well (MQW) structures, modified by insertion of a wide interlayer structure and subsequent growth of differently shaped quantum wells (rectangular, triangular, trapezoidal). This approach of strain management allowed the reduction of dislocation density due to gradually increasing In content in the interlayer and shaping the smooth quantum well/barrier interfaces. A set of c-oriented MQW structures emitting at 470 nm were grown at Vilnius University, Institute of Applied Research, using a closed coupled showerhead type MOCVD reactor. Photoluminescence (PL) spectra of MQW structures were analysed combining continuous wave and pulsed PL measurements. Reactive ion etching of the structures enabled discrimination of PL signals originated in the InGaN interlayer structure, underlying quantum wells, and quantum barriers, thus providing growth-related conditions for enhanced carrier localization in the wells. Time-resolved PL and differential transmission kinetics provided carrier lifetimes and their spectral distribution, being the longest in triangular-shape QWs which exhibited the highest PL intensity. The light-induced transient grating (LITG) technique was used to determine the spatially averaged carrier lifetime in the entire heterostructure, in this way unravelling the electronic quality of the LED internal structure at conditions similar to device performance. LITG decay rates at low and high excitation energy densities revealed increasing with photoexcitation nonradiative recombination rate in the triangular and trapezoidal wells.

Investigating efficiency droop in InGaN/GaN quantum well structures using ultrafast time‐resolved terahertz and photoluminescence spectroscopy

“…It has traditionally been assumed that carriers are not excited in the GaN barrier and buffer layers as the photoexcitation at 400 nm (3.1 eV) is below the band gap energy of GaN (3.51 eV) [18,19]. This assumption is however not valid for our InGaN/GaN MQW structure.…”

Enhancement of quantum efficiency in InGaN quantum wells by using superlattice interlayers and pulsed growth

“…A promising technique for achieving metal rich InGaN layers of good quality is a pulsed growth. This technique was mainly used for InN growth, but it has also been demonstrated as a promising tool for InGaN growth by metal-modulated epitaxy [10], highpressure MOCVD [11,12], and recently by low pressure MOCVD [13].…”