Correlation between optical and electrical properties of Mg-doped AlN epilayers

Abstract

Deep UV photoluminescence and Hall-effect measurements were employed to characterize Mg-doped AlN grown by metal organic chemical vapor deposition. A strong correlation between the optical and electrical properties was identified and utilized for material and p-type conductivity optimization. An impurity emission peak at 4.7eV, attributed to the transition of electrons bound to triply charged nitrogen vacancies to neutral magnesium impurities, was observed in highly resistive epilayers. Improved conductivity was obtained by suppressing the intensity of the 4.7eV emission line. Mg-doped AlN epilayers with improved conductivities predominantly emit the acceptor-bound exciton transition at 5.94eV. From the Hall-effect measurements performed at elevated temperatures, the activation energy of Mg in AlN was measured to be about 0.5eV, which is consistent with the value obtained from previous optical measurements. Energy levels of nitrogen vacancies and Mg acceptors in Mg-doped AlN have been constructed.

Precise lattice location of substitutional and interstitial Mg in AlN

“…within the concentration regime reported for the electrical doping of AlN. 4,14 Quantitative information is obtained by fitting the experimental emission yields with theoretical patterns for the various possible lattice sites, calculated using the manybeam formalism for electron channeling. 20,22 Experimental and theoretical data on the crystallographic structure of AlN and the RT root mean square (rms) displacements of Al and N atoms can be found in Refs.…”

The origin of 2.78 eV emission and yellow coloration in bulk AlN substrates

“…The AlN epilayer and polycrystalline AlN exhibit dominant free exciton ͑FX͒ emission peaks at 5.98 and 5.96 eV, respectively. 8,12,13 However, the FX transition at 5.95 eV and broad emission lines at 4.0 and 2.76 eV have comparable emission intensities in bulk m-AlN. The impurity band around 4.0 eV was previously identified as a donor-acceptor-pair type transition involving a shallow donor and an aluminum vacancy ͑V Al ͒ complex with 2/1 negative charges, either 14 Figure 1͑b͒ compares the 10 K PL spectra of the same set of samples, which shows an obvious blue shift of the FX line to 6.06 ͑6.04͒ eV in the AlN epilayer sample ͑polycrystalline AlN͒.…”

Group-II acceptors in wurtzite AlN: A screened hybrid density functional study

“…8 For practical applications, a hole concentration of at least 10 18 cm −3 is required, while the highest achieved value was about 10 12 cm −3 at room temperature in Mg-doped AlN. 8 Since the ratio of carrier concentration to impurity concentration follows exp͑−E A / k B T͒-where E A is the thermal ionization energy of the acceptor, k B is the Boltzmann constant, and T is the temperature-the main challenge is to find a more appropriate dopant with significant lower thermal ionization energy than for Mg which is about 0.5 eV.…”