Strong Geometrical Effects in Submillimeter Selective Area Growth and Light Extraction of GaN Light Emitting Diodes on Sapphire

Abstract

Advanced semiconductor devices often utilize structural and geometrical effects to tailor their characteristics and improve their performance. We report here detailed understanding of such geometrical effects in the epitaxial selective area growth of GaN on sapphire substrates and utilize them to enhance light extraction from GaN light emitting diodes. Systematic size and spacing effects were performed side-by-side on a single 2” sapphire substrate to minimize experimental sampling errors for a set of 144 pattern arrays with circular mask opening windows in SiO2. We show that the mask opening diameter leads to as much as 4 times increase in the thickness of the grown layers for 20 μm spacings and that spacing effects can lead to as much as 3 times increase in thickness for a 350 μm dot diameter. We observed that the facet evolution in comparison with extracted Ga adatom diffusion lengths directly influences the vertical and lateral overgrowth rates and can be controlled with pattern geometry. Such control over the facet development led to 2.5 times stronger electroluminescence characteristics from well-faceted GaN/InGaN multiple quantum well LEDs compared to non-faceted structures.

High-Quality CrO2 Nanowires for Dissipation-less Spintronics

“…For t g ¼ 45 min, the CrO 2 islands exhibit fully developed facets with smooth surfaces. This type of facet evolution with growth time has been reported recently for SAG of GaN [27]. In addition to the formation of crystalline facets, the extent of lateral overgrowth naturally determines the effective dimensions of the CrO 2 structures.…”

Si Complies with GaN to Overcome Thermal Mismatches for the Heteroepitaxy of Thick GaN on Si

“…In order to eliminate cracking in the Si substrate, we hypothesized that a free Si surface will also dilate the stresses in Si upon cooling down from the GaN growth temperature as supported by thermal stress simulations in Figure d. Therefore, we estimated the lateral overgrowth based on our earlier SAG studies and fabricated structures for which the exposed 500 nm‐thick GaN seed layer is surrounded by an SiO 2 growth mask on top of an isotropically etched Si structure (Figure e and the Experimental Section). This free surface structure (Figure e) resulted in crack‐free GaN layers and Si substrate because the free surface of the Si substrate can accommodate the stress by rotation.…”

InGaN/GaN multiple quantum wells on selectively grown GaN microfacets and the applications for phosphor-free white light-emitting diodes

“…14(a), four different mask geometries with dimensions (windows size, mask size) defined as (2 μm, 4 μm), (4 μm, 2 μm), (5 μm, 5 μm), (3 μm, 7 μm), which were denoted as A, B, C, and D, respectively. After the regrowth of GaN and InGaN/GaN MQWs by MOCVD, the morphologies strongly depended on the mask geometry [80]. It can be seen from Fig.…”