Effect of growth polarity on vacancy defect and impurity incorporation in dislocation-free GaN

Abstract

We have used positron annihilation, secondary ion mass spectrometry, and photoluminescence to study the point defects in GaN grown by hydride vapor phase epitaxy (HVPE) on GaN bulk crystals. The results show that N polar growth incorporates many more donor and acceptor type impurities and also Ga vacancies. Vacancy clusters with a positron lifetime τD=470±50ps were found near the N polar surfaces of both the HVPE GaN layers and bulk crystals.

Defects in Single Crystalline Ammonothermal Gallium Nitride

“…[43,44,79] The observed vacancy concentration is several orders of magnitude higher than what has been reported for HVPE grown material [78,80] and is expected to have a significant effect on the material properties. In GaN, gallium vacancies (V Ga ) and vacancy complexes form deep levels in the band-gap, [44,81,82] cause non-radiative recombination, [83] contribute to sub-bandgap optical absorption, [42] compensate n-type doping, [40] and have been associated with device degradation.…”

“…Especially the incorporation efficiency of oxygen has been reported to be strongly dependent on the growth direction in HVPE and MOVPE grown GaN. [76][77][78] In similar growth conditions the oxygen concentration of HVPE GaN grown in nonpolar and semipolar directions was found to be up to two orders of magnitude higher compared with GaN grown in the c-direction. The oxygen incorporation is expected to depend on the surface density of nitrogen, resulting in high incorporation efficiency on N-rich planes such as N-polar {000-1}, {11-22}, {10-11} and {000-1} and low incorporation efficiency on N-poor planes such as Ga-polar {0001} and {11-20}.…”

“…[78] The gallium vacancy concentration of -c-grown material was found to be over two orders of magnitude higher than that of +c-grown material. The concentration of oxygen was similarly correlated with polarity, suggesting that high oxygen concentration promotes the formation of gallium vacancies or vacancy complexes.…”

“…Also other impurities such as oxygen are known to form complexes with V Ga . [66,78,80] V Ga and their complexes can be detected by positron annihilation spectroscopy [88] and optical absorption measurements in the mid-infrared wavelength range. [43,44,89] …”

“…[88] Positron methods have been widely applied to study vacancy defects in bulk nitride semiconductors, [34,78,80,[90][91][92][93][94][95] including crystals grown by the ammonothermal method. [44,79,96] Positrons implanted into a sample can get trapped in and localize at neutral and negative vacancies due to the missing positive ion core.…”