Investigation of n- and p-type doping of GaN during epitaxial growth in a mass production scale multiwafer-rotating-disk reactor

Abstract

n- and p-doped GaN thin films have been epitaxially grown on c-sapphire substrates by metal-organic chemical-vapor deposition in a production scale multiwafer-rotating-disk reactor. The in situ doping was performed with material having a low background carrier concentration of n∼mid-1016 cm−3. Biscyclopentadienyl magnesium (Cp2Mg) and disilane (Si2H6) were used as the precursors for the p and n dopants, Mg and Si, respectively. The effect of mole flow on material, electrical, and optical properties was studied. We observed that both n- and p-type doped GaN exhibited an excellent surface morphology, even with a high mole flow of doping precursors. After the Mg-doped GaN was annealed in a N2 ambient at ∼700 °C for 30–60 min, the highly resistive GaN was converted into p-type GaN with a low resistance of 0.1–1.0 Ω cm. Transmission electron microscopy showed that the defect density on the annealed Mg-doped GaN is only 4×109 cm−2 which is of the same order as undoped GaN (1.5×109 cm−2). One of the best p-GaN samples has a Hall carrier concentration of 5.2×1018 cm−3 and a hole mobility of 20 cm2/V s, which are the best values reported in the literature to date. The photoluminescence spectra of p-GaN show a strong band edge at 430 nm with a full width at half-maximum of 300 meV at room temperature.

MBE growth and characterization of magnesium-doped gallium nitride

“…These large activation energies result in doping efficiencies at room temperature of little more than 1% (Orton 1995) and this, allied to problems of incorporating large densities of Mg, places severe limits on the p-type conductivity obtainable. The lowest resistivities so far reported (Yuan et al 1995, Nakamura et al 1991 appear to be about 0.06 cm (p = 5×10 18 cm −3 , µ p = 20 cm 2 V −1 s −1 ) and 0.23 cm (p = 3 × 10 18 cm −3 , µ p = 9 cm 2 V −1 s −1 ) but values close to 1 cm are more common and this has led to serious problems with p-type contact resistance in LDs (Orton and Foxon 1998). Shallow, hydrogenic acceptors with ionization energies close to 90 meV appear to exist in GaN but, so far, only for doping levels too low to be of practical use (Ren et al 1996, Dewsnip 1997.…”

p-doping of GaN by MOVPE

“…It is nowadays well established that during the growth process of Mg doped GaN, atomic H is generated from the decomposition of NH 3 and Mg-H complexes are formed in the layer [3] [4] [5]. This has been for instance shown by the occurrence of LO mode in IR absorption, and recently by the observation of the Mg-H local vibration modes (LVM) [4] [14]. Measurements of depth profiles showed that Mg and H are incorporated simultaneously [15].…”

Review—Review of Research on AlGaN MOCVD Growth

“…100 At present, it is generally believed that the Mg-H complex is formed in the epitaxial layer. 92,101,102 However, there is yet to be any relevant study focusing on whether Mg-H has been formed in the gas phase of MOCVD. According to the investigation conducted by the author, the reaction mechanism of dopants in the vapor phase has attracted little attention for study.…”