Unintentional hydrogenation of GaN and related alloys during processing

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Abstract
Atomic hydrogen plays an important role in GaN, passivating the electrical activity of Mg acceptors during cooldown after metal organic chemical vapor deposition growth, and thereby preventing achievement of high p‐type doping levels unless an annealing step is performed. We have found that hydrogen is easily incorporated into GaN and related materials during many different process steps, including boiling in water, wet chemical etching in KOH‐based solutions, dielectric deposition using SiH4 or dry etching in Cl2/CH4/H2Ar electron cyclotron resonance plasmas. In each of these cases we have employed deuterated chemicals and detected the incorporation of deuterium into GaN using high sensitivity secondary ion mass spectroscopy measurements. Hydrogen is found to have a diffusivity of ≳10−11 cm2 s−1 at 170 °C, and to passivate the electrical activity of Mg and C acceptors and also the native shallow donors in InGaN and InAlN. Annealing at 450–500 °C restores the electrical activity, but the hydrogen does not physically leave the films until much higher (∼800 °C) temperatures. The activation energies for dopant reactivation are of the order of 2.5 eV in bulk samples, where hydrogen retrapping is expected to be significant.

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