Selective Area Regrowth Produces Nonuniform Mg Doping Profiles in Nonplanar GaN p–n Junctions

Abstract

Nonplanar GaN p–n junctions formed by selective area regrowth were analyzed using pulsed laser atom probe tomography. Dilute Al marker layers were used to map the evolution of the p-GaN growth interface, enabling extraction of time-varying growth rates for nonpolar, semipolar, and polar surfaces from the trench edge to the center, respectively. The Mg dopant concentration is facet-dependent and varies inversely with the growth rate for the semipolar facets that grow rapidly away from the trench sidewalls. The negligible growth on the vertical sidewall of the trench coincides with an order of magnitude higher Mg concentration and substantial clustering of likely inactive dopants. A high Mg concentration is also observed near the regrowth interface of polar and semipolar planes, which we attribute to etching damage. We conclude that device fabrication processes employing selective area regrowth on nonplanar interfaces should consider both the spatial and temporal dependencies of growth rate that lead to nonuniform doping and explore growth conditions that could reduce variations in growth rate when nonuniform doping would adversely affect device performance.

Morphology Control and Crystalline Quality of p-Type GaN Shells Grown on Coaxial GaInN/GaN Multiple Quantum Shell Nanowires

“…Therefore, it was inferred that Ga diffusion from both the top region and the mask layer supported the rapid growth of the m -plane surface under a high TMG supply and moderate growth temperature. A higher growth rate near the mask mesa than the trench center was also reported in selective p-GaN regrowth on pattern structures and was ascribed to the preferential diffusion of Ga adatoms from the mask region . Regarding the effect of Mg doping, the results indicated that it mainly reduced the growth rate in the c -axis direction without obviously modifying the growth rates on the sidewall of the NWs.…”

“…This is because NWs located outside of the mesa area are allowed to be selectively removed by ultrasonic cleaning. Despite the established growth approaches for MQS-NW structures and their advantages in fabricating devices, a uniform p-GaN shell with high crystalline quality is one of the essential factors for high-performance devices. , The quality of p-GaN is basically associated with the triangular defects or Mg clusters induced by high Mg doping concentration, which has been reported in core–shell MQS NWs. , Nevertheless, Mg doping likewise affects the morphology of GaN on patterned substrates owing to the Mg-induced anisotropic growth rates. , Different structure formations and Mg incorporations of p-GaN were observed in stacked NW structures using selective area growth by molecular beam epitaxy . In the case of core–shell NWs, a small region of the c -plane is inevitably formed at the tip area, which might affect the subsequent p-GaN shell growth and the performance of devices.…”

“…A higher growth rate near the mask mesa than the trench center was also reported in selective p-GaN regrowth on pattern structures and was ascribed to the preferential diffusion of Ga adatoms from the mask region. 26 Regarding the effect of Mg doping, the results indicated that it mainly reduced the growth rate in the c-axis direction without obviously modifying the growth rates on the sidewall of the NWs. As a result, the slow growing c-plane facets appeared to be larger in the NWs with high Mg doping, which was also reported in the literature.…”

“…23,24 Nevertheless, Mg doping likewise affects the morphology of GaN on patterned substrates owing to the Mg-induced anisotropic growth rates. 25,26 Different structure formations and Mg incorporations of p-GaN were observed in stacked NW structures using selective area growth by molecular beam epitaxy. 21 In the case of core−shell NWs, a small region of the c-plane is inevitably formed at the tip area, which might affect the subsequent p-GaN shell growth and the performance of devices.…”

Etched-And-Regrown GaN P–N Diodes with Low-Defect Interfaces Prepared by In Situ TBCl Etching

“…Implant- and diffusion-based selective-area doping (SAD) methods have been actively investigated, − and each faces its respective challenges. Selective-area etching of GaN followed by regrowth or selective-area growth − is intuitively straightforward but has been hampered by the damage and contamination incurred during conventional inductively coupled plasma (ICP) etching. − In the context of etch-and-regrowth, several groups have developed processes to mitigate or repair ICP etching damage with promising results. − Recently, we reported an alternative, in situ etching of GaN with the use of tertiarybutylchloride (TBCl), a Cl-based organometallic precursor. Initial findings indicated that the TBCl etching of GaN has a sufficiently high etch rate and produces minimal damage or contamination. , This etching technique, however, has yet to be tested in working GaN electronic devices.…”