Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Spectroscopic Signature of Local Alloy Fluctuations in InGaN/GaN Multi-Quantum-Disk Light Emitting Diode Heterostructures and Its Impact on the Optical Performance

Soumyadip Chatterjee, Subhranshu Sekhar Sahu, Kanchan Singh Rana, Swagata Bhunia, Dipankar Saha, Apurba Laha

TL;DR

This study investigates how In concentration fluctuations in InGaN/GaN multi-quantum-disk NW LEDs influence carrier localization and optical performance in the green-gap region. Using three PAMBE-grown samples with varying In flux and growth temperature, it combines temperature-dependent PL, power-dependent PL, and TCSPC to connect growth conditions to localization signatures and carrier dynamics. Key findings show stronger localization in samples A and B with S-shaped PL temperature dependence, while sample C exhibits Varshni-like redshift indicating more homogeneous In, along with higher activation energies for nonradiative channels and a PL-excitation exponent near unity (f ≈ 0.939), and longer TCSPC lifetimes (A:263 ps, B:260 ps, C:323 ps). Overall, the work provides guidance on growth-condition optimization to improve green-gap NW-LED performance by mitigating alloy fluctuations and related defects.

Abstract

Inhomogeneity-governed carrier localization has been investigated in three sets of InGaN/GaN multi-quantum-disk light-emitting diode (LED) structures grown by plasma-assisted molecular beam epitaxy (PAMBE) under different process conditions. A temperature-dependent study of the luminescence peak positions reveals that samples prepared under certain process conditions exhibit a thermal distribution of carriers from the localized states that show the typical S-shaped dependence in luminescence characteristics. The absence of an S-shaped nature in the other sample prepared with relatively higher In-flux infers a superior homogeneity in alloy composition. Further investigation manifested superior optical properties for the samples where the S-shape nature is found to be absent.

Spectroscopic Signature of Local Alloy Fluctuations in InGaN/GaN Multi-Quantum-Disk Light Emitting Diode Heterostructures and Its Impact on the Optical Performance

TL;DR

This study investigates how In concentration fluctuations in InGaN/GaN multi-quantum-disk NW LEDs influence carrier localization and optical performance in the green-gap region. Using three PAMBE-grown samples with varying In flux and growth temperature, it combines temperature-dependent PL, power-dependent PL, and TCSPC to connect growth conditions to localization signatures and carrier dynamics. Key findings show stronger localization in samples A and B with S-shaped PL temperature dependence, while sample C exhibits Varshni-like redshift indicating more homogeneous In, along with higher activation energies for nonradiative channels and a PL-excitation exponent near unity (f ≈ 0.939), and longer TCSPC lifetimes (A:263 ps, B:260 ps, C:323 ps). Overall, the work provides guidance on growth-condition optimization to improve green-gap NW-LED performance by mitigating alloy fluctuations and related defects.

Abstract

Inhomogeneity-governed carrier localization has been investigated in three sets of InGaN/GaN multi-quantum-disk light-emitting diode (LED) structures grown by plasma-assisted molecular beam epitaxy (PAMBE) under different process conditions. A temperature-dependent study of the luminescence peak positions reveals that samples prepared under certain process conditions exhibit a thermal distribution of carriers from the localized states that show the typical S-shaped dependence in luminescence characteristics. The absence of an S-shaped nature in the other sample prepared with relatively higher In-flux infers a superior homogeneity in alloy composition. Further investigation manifested superior optical properties for the samples where the S-shape nature is found to be absent.

Paper Structure

This paper contains 4 sections, 3 equations, 6 figures, 1 table.

Table of Contents

  1. Introduction
  2. Experimental Section
  3. Results and Discussion
  4. Conclusion

Figures (6)

  • Figure 1: (a) 45° tilted view and (b) top view FEG-SEM image of an InGaN/GaN multi quantum-disk LED sample grown on Si(111). (b) Annular dark-field STEM image of an isolated nanowire with the 7 bright disk-like regions being the 7 InGaN disks with GaN barriers (darker region) between them.
  • Figure 2: (a) Photoluminescence spectra of the samples at 300K, normalized with respect to characteristic peaks. Characteristic peak emission energy from PL spectra as a function of temperature and for (b) Sample A, (c) Sample B, and (d) Sample C
  • Figure 3: Mechanism of thermal redistribution of carriers in the vicinity of a localization center explaining characteristic red shift and blue shift of emission peak with temperature
  • Figure 4: Integrated PL intensity as a function of temperature for (a) sample A, (b) sample B, (c) sample C and their fitting based on Arrhenius equation
  • Figure 5: Variation of PL intensity with the LASER power at 10 K for (a) sample A, (b) sample B, and (c) sample C with lower exponents of LASER power suggesting higher non-radiative recombination rate
  • ...and 1 more figures