arXiv subjects

Cameron A. Gorsak

Publications and source records attributed to Cameron A. Gorsak.

4 recordsLinked to original sources

arXiv2025

Epitaxial Recovery of beta-Ga2O3 after High Dose Implantation

As an ultrawide bandgap semiconductor, beta-Ga2O3 has been attractive for its strong tolerance to irradiation damage and high n-type conductivity through ion implantation. Homoepitaxial (010) \b{eta}-Ga2O3 films grown by MOCVD were implanted with Ge to study the post-implantation damage and lattice recovery after thermal annealing. Box profiles of 100 or 50 nm at concentration of 5*10^19 or 3*10^19 cm^-3 were formed, with maximum displacement per atom (DPA) of 1.2 or 2.0. Lattice recovery was investigated using X-ray diffraction (XRD) for anneals from 100 C to 1050 C. A gamma-phase related peak was observed for all implant conditions. All samples showed strain relaxation of beta-phase peak at temperature below 500 C, with no significant change for the gamma-phase related peak. For lower damage implants, films recovered fully to epitaxial beta-phase after sequential annealing to 900 C. For the higher damage implant, the gamma-phase associated peak annealed out with increasing temperature, but a new diffraction peak formed at slightly smaller lattice spacing; full recovery of the lattice was not observed until annealing at 1050 C. The newly formed diffraction peak is identified as beta-(20-4), beta-(512), or beta-(71-2), each potentially arising from the conversion of gamma-phase to beta-phase via a common oxygen sub-lattice.

cond-mat.mtrl-sci↗

arXiv2025

Limitations on Activation of High Dose Ge implant in beta-Ga2O3

Among ultrawide bandgap semiconductors, beta-Ga2O3 is particularly promising for high power and frequency applications. For devices, n-type concentrations above 10^19 cm^-3 are required. Ge is a promising alternative n-type dopant with an ionic radius similar to Ga. Homoepitaxial 010 beta-Ga2O3 films were implanted with Ge to form 50 and 100 nm box concentration of 3*10^19 cm^-3 and 5*10^19 cm^-3, with damage ranging from 1.2 to 2.0 displacement per atom. For lower damage implants, optimized anneals in ultrahigh purity N2 at 950-1000 C for 5-10 minutes resulted in Rs of 600-700 omega/sqr, mobilities of 60-70 cm^2/Vs, and Ge activation of up to 40%. For higher damage implants, activation dropped to 23% with similar mobilities. Ge diffusion, measured by second ion mass spectrometry, showed formation of a Ge "clustering peak" with a concentration exceeding the initial implant following anneals in N2 or O2 at 950-1000 C. Beyond this peak, minimal Ge diffusion occurred for N2 anneals at 950 C, but at 1050 C non-Fickian diffusion extended to >200 nm. Electrical activation data suggests that clustered Ge is electrically inactive. To understand Ge clustering, several samples were characterized by synchrotron x-ray diffraction. Second-phase precipitates were observed in as-implanted samples which then fully dissoved after furnace annealing in N2 at 1050 C. Diffraction peaks suggest these implant-induced precipitates may be related to a high pressure Pa-3 phase of GeO2, and may evolve during anneals to explain the Ge clustering. Ultimately, we believe Ge clustering limits activation of implanted Ge at high concentrations.

cond-mat.mtrl-sci↗

arXiv2024

In situ etching of \b{eta}-Ga2O3 using tert-butyl chloride in an MOCVD system

In this study, we investigate in situ etching of \b{eta}-Ga2O3 in a metal-organic chemical vapor deposition (MOCVD) system using tert-Butyl chloride (TBCl). We report the successful etching of both heteroepitaxial (-201)-oriented and homoepitaxial (010)-oriented \b{eta}-Ga2O3 films over a wide range of substrate temperature, TBCl molar flows, and reactor pressures. We identify that the likely etchant is HCl (g) formed by the pyrolysis of TBCl in the hydrodynamic boundary layer above the substrate. The temperature dependence of the etch rate reveals two distinct regimes characterized by markedly different apparent activation energies. The extracted apparent activation energies suggest that at temperatures below ~800 °C the etch rate is likely limited by desorption of etch products. The relative etch rates of heteroepitaxial (-201) and homoepitaxial (010) \b{eta}-Ga2O3 were observed to scale by the ratio of the surface energies indicating an anisotropic etch. For (010) homoepitaxial films, relatively smooth post-etch surface morphology was achieved by tuning the etching parameters.

cond-mat.mtrl-sci↗

arXiv2022

Silicon-doped $β$-Ga$_2$O$_3$ films grown at 1 $μ$m/h by suboxide molecular-beam epitaxy

We report the use of suboxide molecular-beam epitaxy (S-MBE) to grow $β$-Ga$_2$O$_3$ at a growth rate of ~1 $μ$m/h with control of the silicon doping concentration from 5x10$^{16}$ to 10$^{19}$ cm$^{-3}$. In S-MBE, pre-oxidized gallium in the form of a molecular beam that is 99.98\% Ga$_2$O, i.e., gallium suboxide, is supplied. Directly supplying Ga2O to the growth surface bypasses the rate-limiting first step of the two-step reaction mechanism involved in the growth of $β$-Ga$_2$O$_3$ by conventional MBE. As a result, a growth rate of ~1 $μ$m/h is readily achieved at a relatively low growth temperature (T$_{sub}$ = 525 $^\circ$C), resulting in films with high structural perfection and smooth surfaces (rms roughness of < 2 nm on ~1 $μ$m thick films). Silicon-containing oxide sources (SiO and SiO$_2$) producing an SiO suboxide molecular beam are used to dope the $β$-Ga$_2$O$_3$ layers. Temperature-dependent Hall effect measurements on a 1 $μ$m thick film with a mobile carrier concentration of 2.7x10$^{17}$ cm$^{-3}$ reveal a room-temperature mobility of 124 cm$^2$ V$^{-1}$ s$^{-1}$ that increases to 627 cm$^2$ V$^{-1}$ s$^{-1}$ at 76 K; the silicon dopants are found to exhibit an activation energy of 27 meV. We also demonstrate working MESFETs made from these silicon-doped $β$-Ga$_2$O$_3$ films grown by S-MBE at growth rates of ~1 $μ$m/h.

cond-mat.mtrl-sci↗