In situ surface composition and structure of InGaN and GaN thin films by time-of-flight mass spectroscopy of recoiled ions

Time-of-flight mass spectroscopy of recoiled ions (TOF-MSRI) is used to det ermine the surface chemical composition and termination of GaN and InGaN th in films grown by gas source and electron cyclotron resonance molecular bea m epitaxy (GS-MBE and ECR-MBE). We show that using TOF-MSRI all the critica l growth steps, the nitridation, the buffer layer and the epilayers can be optimized in real time, In the case of GS-MBE, the ammonia pressure can be, reproducibly and easily, adjusted to achieve the highest N surface composi tion at the minimum corrosive ammonia flow. For InGaN the total TOF-MSRI io n counts drop with increasing In content. Such an observation can be applie d to evaluate the thin film surface morphology in addition to its surface c omposition. Finally, we present preliminary data showing the use of TOF-MSR I for in situ GaN surface structure determination. We also show that by usi ng a reflectron ion analyzer, much higher ion counts and better resolution can be achieved than a conventional electrostatic sector system. With such a modification, dopant level sensitivities should be achievable and data ra tes compatible with closed loop process control algorithms become possible. (C) 1999 American Vacuum Society. [S0734-211X(99)06503-8].