Growth of p-type and n-type m-plane GaN by molecular beam epitaxy

Abstract

Plasma-assisted molecular beam epitaxial growth of Mg-doped, p-type and Si-doped, n-type m-plane GaN on 6H m-plane SiC is demonstrated. Phase-pure, m-plane GaN films exhibiting a large anisotropy in film mosaic ͑ϳ0.2°full width at half maximum, x-ray rocking curve scan taken parallel to ͓1120͔ versus ϳ2°parallel to ͓0001͔͒ were grown on m-plane SiC substrates. Maximum hole concentrations of ϳ7 ϫ 10 18 cm −3 were achieved with p-type conductivities as high as ϳ5 ⍀ −1 cm −1 without the presence of Mg-rich inclusions or inversion domains as viewed by cross-section transmission electron microscopy. Temperature dependent Hall effect measurements indicate that the Mg-related acceptor state in m-plane GaN is the same as that exhibited in c-plane GaN. Free electron concentrations as high as ϳ4 ϫ 10 18 cm −3 were measured in the Si-doped m-plane GaN with corresponding mobilities of ϳ500 cm 2 / V s measured parallel to the ͓1120͔ direction.

Development and prospects of nitride materials and devices with nonpolar surfaces

“…Directionally dependent Hall effect measurements of m-plane GaN films grown on m-plane SiC substrates reveal strong anisotropy for both electrons and holes (Fig. 14) and thus directly confirmed the theoretical predictions and expectations [5]. The mobility parallel to the [1120] direction was measured as high as ∼11.5 cm 2 /V s (at p∼1.8 × 10…”

“…), being higher than that parallel to the [0001] axes for the same hole concentration [5]. Since the conduction band curvature of GaN shows no significant anisotropy and is insensitive to the strain, the anisotropy in electron mobility was attributed most likely to anisotropic scattering rates being influenced by the presence of a high density of stacking faults and subsequently the formation of band-edge discontinuities in heteroepitaxial polar and semipolar nitrides.…”

“…Another complicating factor in the nitride wurtzite devices grown in the [0001] direction is related to the limitations of p-type magnesium doping levels. The highest reported hole concentrations are only in the range of (1-2) × 10 18 cm -3 [5]. A potential increase of the carrier concentration would lead to a decrease of the contact resistance, a reduction in the p-n junction turn-on voltage and series resistance, and will allow a production of LEDs and LDs with higher optical output efficiency.…”

Electron localization by a donor in the vicinity of a basal stacking fault in GaN

“…Full experimental evidence of such an effect is still lacking, but we can mention, for example, the activation ratios of Si donors at 300 K, which were measured to be comprised between 0.1 and 0.5 in nonpolar GaN layers, 27 whereas this ratio is of 1 in c-plane GaN. Such an incomplete ionization of donors may result from an increased donor binding energy in the presence of BSFs.…”

Impact of nitridation on structural and optical properties of MOVPE‐grown m‐plane GaN layers on LiAlO2

“…These are the absence of spontaneous and piezoelectric polarization leading to higher recombination efficiency in quantum well based light emitting diodes (LEDs) [1] and lasers [2] as well as an eased Mg incorporation enabling higher possible p-type doping levels [3]. Furthermore, the anisotropic crystal structure allows the emission of polarized light and the realization of polarization-sensitive detectors [4,5].…”