Unintentionally Doped GaN Layer Growth

Unintentionally doped GaN layers, 7–24 μm-thick, were grown by HVPE on c-plane sapphire substrates. The concentration of free electrons in these samples is about 1 × 10¹⁷ cm⁻³ at room temperature, as determined from the temperature-dependent Hall effect and time-resolved PL measurements^{17 (link)}. One GaN sample (MD42) from Institut für Physik, Magdeburg, Germany^{4 (link)}, was grown on sapphire by MOCVD and doped with Si and C. The partial etching of GaN was carried out in a Samco inductively coupled plasma (ICP) etching system (model: RIE-101 iPH) with photoresist spr955 serving as a mask. The etching rate was about 40 nm/min under a gas mixture condition of Cl₂/SiCl₄/Ar = 30/5/18 sccm, with the ICP source power and bias power set to 80/30 W and chamber pressure of 0.6 Pa. The etching depth was confirmed by the Veeco Dektak 150 surface profiler.