N-polar InGaN/GaN nanowires: overcoming the efficiency cliff of red-emitting micro-LEDs
Ayush Pandey, Y. Malhotra, Ping Wang, Kai Sun, Xianhe Liu, Zetian Mi
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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m1"> <mml:mrow> <mml:mo form="prefix">∼</mml:mo> <mml:mn>0.75</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>μm</mml:mi> </mml:mrow> </mml:math> , 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m2"> <mml:mrow> <mml:mo form="prefix">∼</mml:mo> <mml:mn>1.2</mml:mn> <mml:mi>%</mml:mi> </mml:mrow> </mml:math> 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.