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Title: Quantum-confined stark effect and polarization field in single quantum well InGaN/GaN LEDs.

Abstract

Based on the wurtzite crystal structure, large (MV/cm) polarization-induced electric fields are known to exist in InGaN single quantum wells (SQWs) grown perpendicular to the GaN c-axis, and these fields may impact optical device performance due to the quantum-confined Stark effect (QCSE). In general, the QCSE has experimentally been found to be smaller than the theoretical value expected for a coherently strained InGaN QW, and subsequently the InGaN/GaN QW polarization field is often under-estimated as well. In this study, we measure the QCSE in modulation-doped, InGaN/GaN SQW LEDs. The well-behaved capacitance-voltage (majority-carrier) characteristics of these devices allow us to unambiguously determine the applied field with bias. With this analysis, we de-couple the QCSE from the QW polarization field and show that although the applied field approaches the opposing QW polarization field theoretical value (i.e., flatband), the QCSE remains too small. We propose a localized-hole picture of the InGaN QW which explains our optical and electrical measurements.

Authors:
; ;
Publication Date:
Research Org.:
Sandia National Laboratories
Sponsoring Org.:
USDOE
OSTI Identifier:
948319
Report Number(s):
SAND2006-0517C
TRN: US200906%%312
DOE Contract Number:
AC04-94AL85000
Resource Type:
Conference
Resource Relation:
Conference: Proposed for presentation at the 2005 Materials Research Society Fall Meeting held November 28, 2005 - December 2, 2005 in Boston, MA.
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CRYSTAL STRUCTURE; ELECTRIC FIELDS; PERFORMANCE; POLARIZATION; QUANTUM WELLS; STARK EFFECT

Citation Formats

Koleske, Daniel David, Kaplar, Robert James, and Kurtz, Steven R. Quantum-confined stark effect and polarization field in single quantum well InGaN/GaN LEDs.. United States: N. p., 2006. Web.
Koleske, Daniel David, Kaplar, Robert James, & Kurtz, Steven R. Quantum-confined stark effect and polarization field in single quantum well InGaN/GaN LEDs.. United States.
Koleske, Daniel David, Kaplar, Robert James, and Kurtz, Steven R. Sun . "Quantum-confined stark effect and polarization field in single quantum well InGaN/GaN LEDs.". United States. doi:.
@article{osti_948319,
title = {Quantum-confined stark effect and polarization field in single quantum well InGaN/GaN LEDs.},
author = {Koleske, Daniel David and Kaplar, Robert James and Kurtz, Steven R.},
abstractNote = {Based on the wurtzite crystal structure, large (MV/cm) polarization-induced electric fields are known to exist in InGaN single quantum wells (SQWs) grown perpendicular to the GaN c-axis, and these fields may impact optical device performance due to the quantum-confined Stark effect (QCSE). In general, the QCSE has experimentally been found to be smaller than the theoretical value expected for a coherently strained InGaN QW, and subsequently the InGaN/GaN QW polarization field is often under-estimated as well. In this study, we measure the QCSE in modulation-doped, InGaN/GaN SQW LEDs. The well-behaved capacitance-voltage (majority-carrier) characteristics of these devices allow us to unambiguously determine the applied field with bias. With this analysis, we de-couple the QCSE from the QW polarization field and show that although the applied field approaches the opposing QW polarization field theoretical value (i.e., flatband), the QCSE remains too small. We propose a localized-hole picture of the InGaN QW which explains our optical and electrical measurements.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}

Conference:
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  • To observe the effects of polarization fields and screening, we have performed contacted electroreflectance (CER) measurements on In{sub 0.07}Ga{sub 0.93}N/GaN single quantum well light emitting diodes for different reverse bias voltages. Room-temperature CER spectra exhibited three features which are at lower energy than the GaN band gap and are associated with the quantum well. The position of the lowest-energy experimental peak, attributed to the ground-state quantum well transition, exhibited a limited Stark shift except at large reverse bias when a redshift in the peak energy was observed. Realistic band models of the quantum well samples were constructed using self-consistent Schroedinger-Poissonmore » solutions, taking polarization and screening effects in the quantum well fully into account. The model predicts an initial blueshift in transition energy as reverse bias voltage is increased, due to the cancellation of the polarization electric field by the depletion region field and the associated shift due to the quantum-confined Stark effect. A redshift is predicted to occur as the applied field is further increased past the flatband voltage. While the data and the model are in reasonable agreement for voltages past the flatband voltage, they disagree for smaller values of reverse bias, when charge is stored in the quantum well, and no blueshift is observed experimentally. To eliminate the blueshift and screen the electric field, we speculate that electrons in the quantum well are trapped in localized states.« less
  • No abstract prepared.
  • Time-integrated and time-resolved microphotoluminescence studies were carried out on In{sub x}Ga{sub 1-x}N quantum disks embedded in GaN nanocolumns grown by molecular beam epitaxy. Emission at {approx}3.33 eV from confined states was detected and observed to blueshift with excitation power; a result of charge screening and the quantum confined Stark effect. The lifetime of the emission was measured to decrease with increasing excitation power, attributed to reduced band bending and resulting increased overlap of the confined electron and hole wave functions.
  • The heat model of a light-emitting diode (LED) with an InGaN/GaN quantum well (QW) in the active region is considered. Effects of the temperature and drive current, as well as of the size and material of the heat sink on the light output and efficiency of blue LEDs are studied. It is shown that, for optimal heat removal, decreasing of the LED efficiency as current increases to 100 mA is related to the effect of electric field on the efficiency of carrier injection into the QW. As current further increases up to 400 mA, the decrease in efficiency is causedmore » by Joule heating. It is shown that the working current of LEDs can be increased by a factor of 5-7 under optimal heat removal conditions. Recommendations are given on the cooling of LEDs in a manner dependent on their power.« less
  • Here, we report on the optical and structural characteristics of violet-light-emitting, ultra-thin, high-Indium-content (UTHI) InGaN/GaN multiple quantum wells (MQWs), and of conventional low-In-content MQWs, which both emit at similar emission energies though having different well thicknesses and In compositions. The spatial inhomogeneity of In content, and the potential fluctuation in high-efficiency UTHI MQWs were compared to those in the conventional low-In-content MQWs. We conclude that the UTHI InGaN MQWs are a promising structure for achieving better quantum efficiency in the visible and near-ultraviolet spectral range, owing to their strong carrier localization and reduced quantum-confined Stark effect.