Origin of background electron concentration in In_xGa _1-xN alloys

The origin of high background electron concentration (n) in In _xGa_1-xN 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_{D 1} = 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. A 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.