Effect of local fields on the Mg acceptor in GaN films and GaN substrates

Abstract

The electron paramagnetic resonance (EPR) spectrum of the Mg acceptor is studied in a variety of GaN samples, including mm-thick free-standing substrates and sub-micron heteroepitaxial films. The former allows a view of the acceptor unique for EPR—in an environment with less than 107 cm−3 dislocations and doping densities ranging from 4 × 1016 to 6 × 1018 cm−3. By probing Mg in a broad range of samples in one study a new feature of the acceptor emerges. The EPR data reveal an anisotropic line shape that reflects a change in the crystal field in the vicinity of the Mg acceptor. This feature must be accommodated by any of the models proposed for the Mg acceptor. Here, we show that one such previously proposed model agrees well with the EPR data obtained from the wide variety of samples studied. The work implies that Mg-doped GaN contains a common Mg-related defect which can be affected by local crystal fields established during growth.

Small non-uniform basal crystal fields in HVPE free-standing GaN:Mg as evidenced by angular dependent and frequency-dependent EPR

“…Thinfilm MOVPE g-factors were determined to be g || = 2.08 and g ⊥ = 1.99 and those of the MME sample, g || = 2.06 and g ⊥ = 2.01. The g-factor anisotropy is consistent with earlier work [12,19,28]. As discussed by others, the g-factor anisotropy seen in the thin-film samples (g || − g ⊥ = 0.09 and g || − g ⊥ = 0.05) compared to the free-standing crystals (g || − g ⊥ ≈ 1.9) reflects a decrease in the local non-axial crystal field Δ x [13,14].…”

“…On the other hand, the line width varies linearly with frequency as the angle between the c axis and applied magnetic field increases, indicating increasing contributions from ∆g ⊥ . The frequency dependence of the linewidth shown in figure 4(b) as well as the variation exhibited at different angles verifies the assumption of g-strain suggested by Zvanut et al, and provides further verification of the crystal field model suggested by Aliev et al [12,19].…”

“…As the HVPE sample cooled after growth, the GaN separated from the substrate due to thermal stress and was polished, resulting in free-standing GaN doped with 3.0 × 10 18 cm −3 Mg. The detailed growth process and additional characterization was described previously [16][17][18][19].…”

“…In earlier work, a non-uniformity of the crystal field was deduced from an analysis of the angular dependent line shape. The study assumed that a non-zero distribution of g-factors (Δg), known as g-strain, caused the angular dependent line shape [12,19,30]. Each different g-factor, expressed as g i , within the distribution of g-factors shifts the magnetic field resonance.…”

Energy Stored and Capacitance of a Circular Parallel Plate Nanocapacitor

“…At this juncture, we also point out that the results obtained thus far can also be helpful to gauge the accuracy of various theoretical approximations and numerical methods used to study the properties of systems with circular symmetry. This situation may apply to certain 2D compositions formed in semiconductor quantum dots, heterostructures or thin films [ 54 , 55 , 56 , 57 ] which lead to the creation of a two-dimensional electron gas (2DEG) system. In particular, the physics of quantum Hall effect (QHE) has at its heart the model of a 2D system of electrons confined in a neutralizing background represented by a uniformly charged circular disk lying on the same plane as the layer of electrons [ 58 , 59 , 60 , 61 , 62 , 63 ].…”