Fabrication of low-curvature 2 in. GaN wafers by Na-flux coalescence growth technique

Abstract

Low-curvature and large-diameter GaN wafers are in high demand for the development of GaN-based electronic devices. Recently, we have proposed the coalescence growth of GaN by the Na-flux method and demonstrated the possibility of enlarging the diameter of high-quality GaN crystals. In the present study, 2 in. GaN wafers with a radius of curvature larger than 100 m were successfully produced by the Na-flux coalescence growth technique. FWHMs of the 002 and 102 GaN X-ray rocking curves were below 30.6 arcsec, and the dislocation density was less than the order of 102 cm−2 for the entire area of the wafer.

Evaluation of lattice curvature and crystalline homogeneity for 2-inch GaN homo-epitaxial layer

“…24,25 Several groups have artificially fabricated dot-patterns and grown seed layers by the HVPE method to improve crystallinity. [26][27][28] GaN substrates grown by HVPE methods have high crystalline quality; however, freestanding GaN substrates feature lattice curvature owing to internal stresses, such as compressive and tensile stress. The lattice curvature and dislocation degrades the device performance.…”

Development of GaN substrate with a large diameter and small orientation deviation

“…We grew approximately 500‐µm‐thick GaN on a high‐quality GaN substrate prepared by Na‐flux with a multipoint‐seed coalescence (MPSC) method . Many cracks, concentrated dislocations (≥ 10 7 cm −2 ), and significant warping (curvature radius <1 m) were generated.…”

“…However, it is not easy to achieve a high quality throughout the entire area . On the other hand, a liquid phase growth (LPG) method, such as the respective Na‐flux and ammonothermal methods , can easily realize high‐quality substrates. Currently, however, LPG cannot easily grow GaN crystals with a large diameter.…”

Growth of Bulk Nitrides from a Na Flux

“…In 2013, coalescence growth, which is a technique to effectively enlarge the diameter of GaN crystals by coalescing GaN crystals grown from many isolated point seeds, was developed [43][44][45]. Schematic illustration of the coalescence growth process is shown in Figure 13.26.…”

“…A multipoint-seed-GaN substrate (MPS-GaN sub.) In general, etch pits resulting from etching in a NaOH-KOH solution are considered to come from dislocations [41][42][43][44]46,47]. Point seeds were arranged in a hexagonal pattern so that the coalescence direction corresponded to the a-direction of the GaN.…”