(11-22) semipolar InGaN emitters from green to amber on overgrown GaN on micro-rod templates

Abstract

We demonstrate semipolar InGaN single-quantum-well light emitting diodes (LEDs) in the green, yellow-green, yellow and amber spectral region. The LEDs are grown on our overgrown semipolar (11-22) GaN on micro-rod array templates, which are fabricated on (11-22) GaN grown on m-plane sapphire. Electroluminescence measurements on the (11-22) green LED show a reduced blue-shift in the emission wavelength with increasing driving current, compared to a reference commercial c-plane LED. The blue-shifts for the yellow-green and yellow LEDs are also significantly reduced. All these suggest an effective suppression in quantum confined Stark effect in our (11-22) LEDs. On-wafer measurements yield a linear increase in the light output with the current, and external quantum efficiency demonstrates a significant improvement in the efficiency-droop compared to a commercial c-plane LED. Electro-luminescence polarization measurements show a polarization ratio of about 25% in our semipolar LEDs.

Defect reduction in overgrown semi-polar (11-22) GaN on a regularly arrayed micro-rod array template

“…It is worth noting that a very small number of extra dislocations are generated due to the 2nd coalescence. Our plan-view TEM image indicates that the overall dislocation density in our overgrown (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) semi-polar GaN is about 4.2×10 8 cm −2 , demonstrating a significant reduction in dislocation density from the order of 10 10 cm −2 in the as-grown GaN which is used to fabricate into the micro-rod array template. Basal stacking faults (BSFs), as extended defects, can be observed along either the [-12-10] or the [2-1-10] zone-axis by tilting 30 • from the [1-100] zone-axis.…”

“…The overgrowth initiates from the exposed sidewalls of micro-rods as shown in Figure 1(b), and the lateral growth is dominated by the growth along the [0001] direction labelled as c-direction and the [11][12][13][14][15][16][17][18][19][20] direction labelled as a-direction. Comparing the lengths of the two growing wings, the c-direction growth is faster than the a-direction growth.…”

“…On such high quality semi-polar GaN templates, we have achieved high performance semi-polar light emitting diodes (LEDs) with a wide spectral range of up to amber. 16,17 In this letter, we investigate in detail a mechanism of the defect reduction in the overgrown semi-polar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN on the regular micro-rod array templates by transmission electron microscopy (TEM) measurements, and a detailed model has been established, essentially allowing us to further improve the crystalline quality of overgrowth semi-polar GaN on sapphire.…”

“…A single (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN layer with a thickness of 1.3 µm is grown on m-plane sapphire using our high temperature AlN buffer by metal organic chemical vapor deposition (MOCVD). 18 For subsequent overgrowth, mask-patterned micro-rod arrays have been fabricated on the semi-polar GaN layer.…”

“…One clear way forward, meeting the fundamental challenges, is to grow along a semi-polar direction, in particular, [11][12][13][14][15][16][17][18][19][20][21][22] direction. It has been predicted that (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) surface leads to easier accommodation of larger indium atoms than either polar-or non-polar surface, 4 favoring the growth of high indium content InGaN layers which are necessary for green or yellow emitters.…”