Highly conductive Ge-doped GaN epitaxial layers prepared by pulsed sputtering

Abstract

Highly conductive Ge-doped GaN epitaxial layers were grown by low-temperature pulsed sputtering, and their fundamental structural and electrical properties were investigated. The room-temperature (RT) electron concentration was increased to 5.1 × 1020 cm−3 by the Ge doping, and the atomically flat stepped and terraced surface and the crystalline quality of the layers were maintained. Consequently, the RT resistivity was reduced to 0.20 mΩ·cm, which is comparable to that for typical transparent conductive oxides such as indium tin oxide. The contact resistance of Ge-doped GaN with a Ti/Al/Ti/Au metal stack prepared without annealing was as low as 0.087 Ω·mm. Furthermore, the selective formation of a Ge-doped region using an SiO2 mask was demonstrated. The results clearly indicate the strong potential of pulsed sputtering Ge-doped GaN growth for forming low-parasitic-resistance contact layers of various electrical and optical devices.

Electron transport properties of degenerate n-type GaN prepared by pulsed sputtering

“…3(a), which was calculated from the combination of the polar optical phonon, deformation potential acoustic phonon, and piezoelectric phonon scattering. 13 Here, the dislocation scattering for degenerate GaN proposed by Look et al 18 was ignored because it is quite small in our samples. The experimental mobility data were fitted by Mattisen's rule (µ total 1 = µ Lattice 1 + µ I.I.…”

“…[6][7][8][9][10][11] PSD is suitable for growing heavily impurity-doped GaN because of its highly nonequilibrium nature. In fact, heavily Si-doped GaN prepared by PSD exhibited a RT electron 13 These achievements in the growth of highly conductive, heavily doped n-type GaN provide a good opportunity for systematically investigating the transport properties of degenerate GaN. Here, we have investigated the dopant concentration dependence of the electrical properties of highly Ge-and Si-doped GaN epilayers prepared by PSD using secondary-ion mass spectrometry (SIMS) and temperature-dependent Hall-effect measurements.…”

“…The details of the growth procedure have been reported elsewhere. 12,13 To investigate their electrical properties, we deposited the n-type doped GaN epilayers onto commercially available semi-insulating C-doped GaN templates on sapphire as starting substrates. The dislocation density of the GaN templates was typically 5.0 × 10 9 cm 2 .…”

Numerical Investigation of the Impact of ITO, AlInN, Plasmonic GaN and Top Gold Metalization on Semipolar Green EELs

“…However, in the plasmonic GaN, the strain increases with the increasing doping concentration. Although for 5 × 10 20 cm −3 the compressive strain is as low as 0.26% [23], the thickness of these layers is as large as 0.20 µm, and when no tensile strained layers are used that could compensate that strain, the lattice defects (not considered in our calculations) are generated, which leads to the degradation of laser characteristics. These problems do not arise, when n-AlInN layer is introduced in the n-cladding, due to the fact that for indium content of 17% this material is lattice-matched to GaN.…”

“…Figure 7 shows the threshold current densities calculated for EELs with plasmonic GaN layers of thicknesses and free carrier concentrations in the ranges of 0.1-0.5 µm and 1-5 × 10 20 cm −3 , respectively. The maximum in the latter range is based on data reported in [23]. An increase in the free carrier concentration of the plasmonic layer resulted in a decrease in both its optimal thickness and that of the n-GaN spacer, while the optimal ITO thickness increased (Table 4).…”