Low-dislocation-density GaN from a single growth on a textured substrate

Abstract

(Received s The density of threading dislocations (TD) in GaN grown directly on flat sapphire substrates *m is typically greater than 109/cm2. Such high dislocation densities degrade both the electronic so and photonic properties of the material. The density of dislocations can be decreased b~~@ orders of magnitude using cantilever epitaxy (CE), which employs prepattemed sapphire substrates to provide reduced-dmension mesa regions for nucleation and etched trenches ($)42 between them for suspended lateral growth of Gall or AIGaN. The substrate k prepattemed d~w ith narrow lines and etched to a depth that permits coalescence of laterally growing III-N~@ nucleated on the mesa stiaces before vertical growth fills the etched trench. Low a dislocation densities typical of epitaxial lateral overgrowth (ELO) are obtained in the cantilever regions and the TD density is also reduced up to 1 micrometer from the edge of the support regions.The great potential of wide-band-gap Group III nitrides (III-N) has been limited in many applications by the very high density of treading dislocations (TDs) that form when the III-N materials are grown on latticemismatched substrates [1]. Growth of GaN on a planar substrate of sapphire, SiC, orSi(111) produces TD areal densities on~e order of 108to 1010/cm2.Although such high TD densltles do not appear to seriously degrade light-emitting diode (LED) performance due to the vertical character of the TDs and the short minority carrier difision lengths found in III-nitrides, they cause unacceptably short lifetimes for laser diodes (LDs) and excessive leakage current under reverse bias for p-n junction devices such as field-effect transistors (FETs) and high-electron-mobility transistors (HEMTs). To solve these problems, a GaN substrate with <1OG TDs/cm2 will be required.Several approaches have achieved considerable success in reducing TD densities to the 106/cm2range in selected regions of a wafer, but these techniques are very time-consuming to implement. These include epitaxial lateral overgrowth (ELO or LEO) [2,3], pendeoepitaxy (PE) [4], and lateral overgrowth from trenches (LOFT) [5]. While each technique produces selective areas on a wafer that possess the low TD densities (<l O'/cm*)required for electronic and longlived laser devices, they are complex, multistep processes requiring ex-situ deposition and etching of dielectric masks and regrowth. In each case, broad-area GaN is first grown on a (0001) sapphre, (0001) 6H-SiC, or Si(l 11) substrate; this initial GaN layer displays the typical 108-10*0/cm2TD density characteristic of standard GaN epitaxial layers and serves as the seed region for subsequent GaN regrowth. GaN grown directly over the seed region retains the inhial high TD density while regions of lateral growth over the dielectric mask in ELO or from etched GaN walls in PE and LOFT display reduced TD densities. High concentrations of TDs are generally observed at the mask edges and both TDs and voids are common at the coalescence front over the dielectric mask.We report a ...

Nano-scale optical and electrical probes of materials and processes.

“…7,8 After deposition and annealing of a thin GaN nucleation layer and deposition of a thin GaN layer at 1050°C, the GaN growth temperature is decreased to 950°C to produce pyramidal facets (112-2) on top of the sapphire line. After the pyramidal facets are well formed, the GaN, as shown in Fig.…”

High Al-Content AlInGaN Devices for Next Generation Electronic and Optoelectronic Applications

“…Such high dislocation densities degrade both the electronic and photonic properties of the material. The density of dislocations can be decreased by orders of magnitude using cantilever epitaxy (CE) [1] , which employs prepatterned sapphire substrates to provide reduced-dimension mesa regions for nucleation and etched trenches between them for suspended lateral growth of GaN or AlGaN. The substrate is prepatterned with narrow lines and etched to a depth that permits coalescence of laterally growing III-N nucleated on the mesa surfaces before vertical growth fills the etched trench.…”

Development of Key Technologies for White Lighting Based on Light-Emitting Diodes (LEDs)

“…Cantilever Epitaxy (CE) was invented at Sandia just before the initiation of this program [1]. This prior work showed that greatly reduced dislocation densities were possible with this method.…”

“…After some initial tests we also decided to add emissivity correction to this pyrometer, using the basic approach described by Breiland [1]. Some aspects of the hardware and software are different for the…”