Search by keywords or author
• Photonics Research
• Vol. 10, Issue 4, 04001107 (2022)
A. Pandey1, Y. Malhotra1, P. Wang1, K. Sun2, X. Liu1, and Z. Mi1、*
Author Affiliations
• 1Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109, USA
• 2Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA
• show less
A. Pandey, Y. Malhotra, P. Wang, K. Sun, X. Liu, Z. Mi. N-polar InGaN/GaN nanowires: overcoming the efficiency cliff of red-emitting micro-LEDs[J]. Photonics Research, 2022, 10(4): 04001107 Copy Citation Text show less

Abstract

A high efficiency, high brightness, and robust micro or sub-microscale red light emitting diode (LED) is an essential, yet missing, component of the emerging virtual reality and future ultrahigh resolution mobile displays. We report, for the first time, to our knowledge, the demonstration of an N-polar InGaN/GaN nanowire sub-microscale LED emitting in the red spectrum that can overcome the efficiency cliff of conventional red-emitting micro-LEDs. We show that the emission wavelengths of N-polar InGaN/GaN nanowires can be progressively shifted from yellow to orange and red, which is difficult to achieve for conventional InGaN quantum wells or Ga-polar nanowires. Significantly, the optical emission intensity can be enhanced by more than one order of magnitude by employing an in situ annealing process of the InGaN active region, suggesting significantly reduced defect formation. LEDs with lateral dimensions as small as $∼0.75 μm$, consisting of approximately five nanowires, were fabricated and characterized, which are the smallest red-emitting LEDs ever reported, to our knowledge. A maximum external quantum efficiency $∼1.2%$ was measured, which is comparable to previously reported conventional quantum well micro-LEDs operating in this wavelength range, while our device sizes are nearly three to five orders of magnitude smaller in surface area.

1. INTRODUCTION

Sub-micrometer and nanoscale optoelectronic devices, including light emitting diodes (LEDs) and laser diodes, have drawn considerable attention, as they are essential for future large scale, or ultra-large scale integration of electronic and optoelectronic devices on a single chip. To date, however, it has remained extremely challenging to achieve high efficiency micro or nanoscale optoelectronic devices. One noticeable example is the efficiency cliff related to micro-LEDs, i.e., a drastic reduction in device efficiency with reducing dimensions. Micro-LEDs have been considered as the essential building block for emerging virtual/augmented reality devices and systems, due to their ultrahigh brightness, low power consumption, ultrahigh integration density, superior stability, and long lifetime. Shown in Fig. 1, external quantum efficiency (EQE) in the range of 50%–70% has been commonly measured for AlGaInP-based large area LEDs (lateral dimensions $>100 μm$), whereas the efficiency drops to negligible values for devices with lateral dimensions of the order of 10 μm.

Copy Citation Text
A. Pandey, Y. Malhotra, P. Wang, K. Sun, X. Liu, Z. Mi. N-polar InGaN/GaN nanowires: overcoming the efficiency cliff of red-emitting micro-LEDs[J]. Photonics Research, 2022, 10(4): 04001107