The origin of high background electron concentration (n) in In x Ga 1-x N alloys has been investigated. A shallow donor was identified as having an energy level (E D1 ) that decreases with x (E D1 =16 meV at x=0 and E D1 =0 eV at x ∼ 0.5) and that crossover the conduction band at x ∼ 0.5. This shallow donor is believed to be the most probable cause of high n in InGaN. This understanding is consistent with the fact that n increases sharply with an increase in x and becomes constant for x > 0.5.

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... continuous reduction in n was obtained by increasing the V/III ratio during the epilayer growth, suggesting that nitrogen vacancy related impurities are a potential cause of the shallow donors and high background electron concentration in InGaN.