The effect of carbon impurities on lightly doped MOCVD GaN Schottky diodes

Schottky diodes have been fabricated on metalorganic chemical vapor deposition GaN epitaxial layers grown on sapphire substrates. Carbon impurities limit the ability of these films to be used in high-power devices. Although its effect can be mitigated by growing the films at higher pressure, higher flow rates, and larger V/III ratios, it still effectively limits the net carrier concentration to ∼1016 cm−3 and therefore the breakdown voltage to ∼1200 V by acting as a compensating deep acceptor for n-type material. The net carrier concentration is smaller than the carbon concentration indicating that not all of the carbon occupies a nitrogen site acting as a deep acceptor. It is not known whether some of the carbon occupies gallium sites acting as a donor, interstitial sites creating states in the midgap region, and/or is tied up in the large number of dislocations in the films where it is not electrically active.