High-power low-droop violet semipolar (303¯1¯) InGaN/GaN light-emitting diodes with thick active layer design

Abstract

Devices grown on nonpolar and semipolar planes of GaN offer key performance advantages over devices grown on the conventional c-plane, including reduced polarization fields. This allows for a wider design space on semipolar planes for light emitting diodes (LEDs) to address the problem of efficiency droop at high current densities. LED structures with very thick (10–100 nm) InGaN single-quantum-well/double heterostructure active regions were grown using conventional metal organic chemical vapor deposition on semipolar (303¯1¯) free-standing GaN substrates and processed and packaged using conventional techniques. Simulated band diagrams showed reduced polarization fields on the (303¯1¯) plane. The calculated critical thickness for misfit dislocation formation is higher on the (303¯1¯) plane than on other semipolar planes, such as (202¯1¯), allowing for thicker active regions than our previous work to further reduce droop. The higher critical thickness was confirmed with defect characterization via cathodoluminescence. A trend is demonstrated in lower efficiency droop for devices with thicker active regions. Thermal droop characteristics of these devices are also presented. These observed results were utilized to demonstrate over 1 W of output power at a current density of 1 kA/cm2 from a single 0.1 mm2 LED device.

Complete orientational access for semipolar GaN devices on sapphire

“…with zone axis of [] and g = and g = 0002, reveals dislocation contrast of a ‐ and c ‐type, respectively, and the former also revealing partial dislocations associated with basal plane stacking faults. In the g = image, the straight line contrast originating from the growth sidewall up at an angle of ∼15° from vertical are confined to the basal plane, and are attributed to the presence of I1‐type stacking faults . The rest of the crystal shows a lower density of defects, with short threading segments appearing, indicating dislocations propagating in the out‐of‐plane direction.…”

“…This explains the absence of these orientations as surfaces for planar device layer growth prior to the development of controlled slicing and polishing process on bulk substrates. Overall, notable demonstrations in the semipolar field using these high quality bulk substrates have included the first direct emission true green laser diode in 2009 on the () orientation , yellow LEDs on the () orientation with higher temperature stability than with the AlInGaP family of LEDs, and very low droop violet‐blue LEDs on the () and () orientations .…”

“…We performed a complete survey of the device literature on semipolar and non‐polar devices to date, with data obtained from Refs. . To extract the overall trends over this past decade of work, the device performance of the best reported devices are plot as a function of orientation in Fig.…”

“…Reported device performance from Refs. (left). Maximum emission wavelength reported from an LED for each orientation, and characteristics of best violet‐blue emitting LED device, light output power at 20 mA, maximum EQE, and electroluminescence FWHM.…”

Green emission from semipolar InGaN quantum wells grown on low‐defect () GaN templates fabricated on patterned r‐sapphire

“…To address the issue of QCSE and efficiency droop at high current density, LEDs can be grown in a direction different from the c ‐axis in order to alleviate the polarization field across the QWs. Moreover, the absence of polarization allows potentially to grow thicker QWs which is favorable for reducing efficiency droop . Therefore, semipolar and nonpolar nitrides look very promising for the realization of high efficiency opto‐electronic devices.…”