| Abstract Scope |
III-Nitrides grown along non-polar orientations, e.g. m-plane [10-10] and a-plane [11-20], are attracting great attention, due largely to mitigation of the Quantum Confine Stark Effect, leading to increased internal quantum efficiency. However, due to differences in growth surface structure, the change in crystal growth orientation could also affect intrinsic and extrinsic defect formation, which can impact device properties. To date, information on traps in non-polar nitrides is relatively sparse. Hence, here we are exploring the influence of crystal orientation on trap incorporation within m-plane GaN grown by ammonia-based molecular beam epitaxy (MBE) utilizing Deep Level Optical Spectroscopy (DLOS) and Deep Level Transient Spectroscopy (DLTS). To isolate the impact of crystal orientation, c-plane and m-plane GaN substrates, with dislocation densities of ~1×10<SUP>8</SUP>cm<SUP>-2</SUP> and ~1×10<SUP>6</SUP>cm<SUP>-2</SUP>, respectively, were “co-loaded” in the MBE chamber followed by identical epitaxial growth. P<SUP>+</SUP>-n structures were grown to support capacitance-based DLOS/DLTS, with Mg doping of 1×10<SUP>20</SUP>cm<SUP>-3</SUP> and Si doping of 1×10<SUP>17</SUP>cm<SUP>-3</SUP>, to provide sensitivity to the n-side of the junction. However, C-V revealed that the Si-doped layer of the m-plane sample possessed a higher effective doping concentration of ~ 1×10<SUP>18</SUP>cm<SUP>-3</SUP>, which was correlated with SIMS data that revealed a higher oxygen incorporation, which act as residual donors, as has been observed in earlier work on m-plane GaN.<SUP>[1]</SUP> By fitting the DLOS optical cross sections, three traps were revealed in both samples at Ec-1.3eV, Ec-2.6eV and Ec-3.3eV. These levels closely match earlier reports for point defects associated with interstitial carbon, gallium vacancies, and C<SUB>N</SUB> substitutionals, respectively.<SUP>[2]</SUP> Steady state photo-capacitance showed that the traps at Ec-2.6eV and Ec-3.3eV possess nearly two orders of magnitude higher concentration in m-plane (3.2×10<SUP>16</SUP>cm<SUP>-3</SUP> and 2.3×10<SUP>16</SUP>cm<SUP>-3</SUP>) GaN versus c-plane (6.5x10<SUP>14</SUP>cm<SUP>-3</SUP> and 9.0x10<SUP>14</SUP>cm<SUP>-3</SUP>) GaN. Similarly, DLTS results also suggest that the m-plane n-GaN layer has a higher concentration of Ec-2.6eV state, which for DLTS appears as a hole trap at Ev+0.8eV, and was observed only in the m-plane sample. Since the dislocation density of the m-plane substrate is ~ two orders of magnitude lower than that of the c-plane substrate, this trend cannot be ascribed to dislocation density. The likely source for the increased defect incorporation may be related to differences in surface growth dynamics for these crystal orientations, although due to the higher oxygen donor concentration for the m-plane sample, the influence of the Fermi level on defect formation energy cannot be discounted. We are currently exploring this in greater detail with respect to systematically varied growth parameters, especially ammonia flux, and this will be reported in a comparative fashion for both crystal orientations. |