MBE growth and characterization of magnesium-doped gallium nitride

Abstract

We describe measurements of the electrical and luminescence properties of Mg-doped GaN films grown by plasma-enhanced molecular beam epitaxy on sapphire and GaAs substrates. Secondary ion mass spectroscopy measurements were used to determine the total Mg concentration in each of the films and showed the Mg profiles to be flat throughout the films. At low Mg beam fluxes, there is a linear relationship between the Mg concentration in the film [Mg] and the Mg flux but, for fluxes above about 10 −2 ML s −1 , [Mg] saturates at 2 × 10 19 cm −3 (at a growth temperature of 750 • C). We outline a simple model of Mg incorporation which explains the experimental data. Hall effect measurements reveal that p-type conductivity is obtained only in films grown under slightly nitrogen-rich conditions and demonstrate that, in thin films (< 1 µm), conductivity is dominated by high densities of donor-type defects. This is also borne out by photoluminescence (PL) results. Most of the samples showed bound exciton emission at low temperatures, in some cases involving neutral donors, in others neutral acceptors, the D 0 X emission suggesting that the incorporation of Mg results in a lowering of the GaN band gap. All samples show donor-acceptor recombination and detailed analysis suggests that Mg doping suffers from self-compensation. Room-temperature PL is dominated by a free electron-bound hole emission line at 3.2 eV in p-type samples but by deep emission in samples grown under Ga-rich conditions.

Growth of GaN:Mg crystals by high nitrogen pressure solution method in multi-feed–seed configuration

“…This result suggests a decreasing concentration of Mg in the crystals with increasing growth temperature. A similar relation between Mg content in GaN crystals and the character of the corresponding low temperature PL spectra has been clearly shown elsewhere [13]. The concentrations of both magnesium acceptors and oxygen donors have to be more precisely measured by SIMS for further interpretation of the PL behavior in the GaN:Mg crystals grown in this study.…”

Polarity control during molecular beam epitaxy growth of Mg-doped GaN

“…11 Several groups have also re-ported linear incorporation of Mg below the flux required for saturation. 12,13 Further, for a given Mg flux, the incorporated Mg concentration increases exponentially for a decrease in substrate temperature. The finding of the saturated incorporation rate suggested that Mg incorporation takes place via a surface phase accumulation or via particular crystal sites.…”

Defect-engineered GaN:Mg nanowire arrays for overall water splitting under violet light

“…[15][16][17] With further increase in Mg flux (T Mg ¼ 260 C), a new broad emission peak centered at $2.95 eV is clearly revealed. This peak is attributed to the donor-acceptor-pair (DAP) transition 18 and shallow Mg acceptor states. The Mg-related acceptor level is located at $220 meV above the valence band.…”