Demonstration of device-quality 60% relaxed In0.2Ga0.8N on porous GaN pseudo-substrates grown by PAMBE

Abstract

Achieving high-quality, relaxed InGaN substrates for longer-wavelength light emitting diodes (LEDs) is of great interest for the development of micro-LED based display technology. This work demonstrates molecular beam epitaxy (MBE)-grown In0.2Ga0.8N with a strain relaxation of 60% corresponding to an equivalently fully relaxed In composition of 12%. This was done by growing on a GaN-on-porous GaN pseudo-substrate (PS). The surface morphology of this film was found to be free of V-defects on the surface and with a threading dislocation density comparable to that of the GaN layers beneath. While InGaN grown on planar GaN-on-sapphire substrates remained nearly strained to the GaN underlayer, InGaN grown under identical conditions on PS displayed elastic-like relaxation. Furthermore, an increase in indium (In) composition was observed for the InGaN grown on PS. Where past work of InGaN grown on porous GaN PS by metalorganic chemical vapor deposition also resulted in relaxed InGaN templates suitable for device application, the surfaces of these relaxed films exhibited V-defects for thicker layers. Employing MBE, thicker films with higher In composition can be achieved with smooth surface morphology, thus enabling pseudo-substrates with a wide range of lattice constants. These pseudo-substrates of varying in-plane lattice constant are attractive for III-nitride based optoelectronics, particularly for green, amber, and red micro-LEDs.

Demonstration of 82% relaxed In0.18Ga0.82N on porous GaN pseudo-substrate by plasma-assisted molecular beam epitaxy

“…On the other hand, samples with ∼1μm-thick InGaN (samples A3 and B3) showed an increase in spiral hillock density, indicating an increase in the dislocation density. Interestingly, none of the samples showed V-defects, pits or cross-hatching like features on the surface which were observed previously in InGaN films grown on GaN PS by MOCVD or PAMBE [27,38].…”

“…The process flow to obtain the final relaxed InGaN layers grown on PS (figure 1) is as follows: (i) patterning of 10 μm × 10 μm tiles and 6 μm × 6 μm tiles of GaN on Si substrates; (ii) porosification of GaN:Si layer by EC etching; and (iii) PAMBE growth of GaN/ InGaN. The electrochemical etching and sample preparation for PAMBE growth was described in details elswhere [31,38].…”

“…In addition, the lower growth temperatures in the MBE growth process compared to that of the MOCVD process can be useful to increase the In content in the InGaN films. Notably, regrowth of InGaN on porous GaN by molecular beam epitaxy has recently been reported by Wurm et al [38]. An extensive study of InGaN regrowth on porous GaN by MBE is still to be performed.…”

Fully Relaxed, Crack-Free AlGaN with upto 50% Al Composition Grown on Porous GaN Pseudo-Substrate

“…Reciprocal space maps (RSMs) were taken using XRD around the GaN (1 1 24) reflection. Composition and relaxation were determined from these RSMs using X-Pert Epitaxy software [44,45].…”

Behaviors of AlGaN Strain Relaxation on a GaN Porous Structure Studied with d-Spacing Crystal Lattice Analysis

“…In this process, the etching direction essentially follows the flow of electric current for forming subsurface lateral pores in GaN. Many applications based on GaN or AlGaN PSs have been explored, including the improvements of LED crystal quality and light extraction [ 9 , 10 , 11 , 12 , 13 ], the liftoff of a GaN layer or an LED structure from its substrate [ 14 , 15 , 16 ], the enhancement of water-splitting efficiency [ 17 , 18 ], the formation of a distributed Bragg reflector [ 19 , 20 ], the increase in sensor sensitivity [ 21 ], the relaxation of strain [ 22 ], and the fabrications of lateral and vertical laser diodes [ 23 , 24 , 25 ]. More applications are expected to be developed based on such a subsurface PS.…”