AVS 51st International Symposium
    Science of Semiconductor White Light Topical Conference Wednesday Sessions
       Session WL+MS-WeA

Invited Paper WL+MS-WeA9
Emissivity-Correcting Pyrometry for Group-III Nitride MOCVD

Wednesday, November 17, 2004, 4:40 pm, Room 304B

Session: Science of Semiconductor White Light II
Presenter: J.R. Creighton, Sandia National Laboratories
Authors: J.R. Creighton, Sandia National Laboratories
C.C. Mitchell, Sandia National Laboratories
Correspondent: Click to Email
Accurate temperature measurement during group-III nitride MOCVD is very difficult due to the broad spectral transparency of the substrates and epitaxial layers. In fact, there is no readily available method that measures the true surface temperature during deposition. We have developed a pyrometer that operates near the high-temperature bandgap of GaN, thus solving the transparency problem once a ~1 micron thick GaN epilayer has been established. At typical GaN MOCVD conditions the RMS temperature noise of the system is <0.1°C. By simultaneously measuring the reflectance, we can also correct for emissivity changes when films of differing optical properties (e.g. AlGaN) are deposited on the GaN template. By employing the virtual interface method, the reflectance measurement can also be used to monitor growth rates and compute optical properties of the thin films. Using this method we have measured the high temperature optical constants of GaN at the effective pyrometer wavelength (405 nm). Near 1000°C, the imaginary part (k) of the GaN refractive index is ~0.2, thus demonstrating that the epilayer is opaque. Small artifacts (due to stray light) in the emissivity-correction method are often observed, leading to residual oscillations in the corrected temperature. For our new nitride pyrometer the residual temperature oscillations are typically <3°C in amplitude when growing AlN/GaN heterostructures. Through proper calibration experiments, the nature of the error can be understood and quantitatively eliminated. We will also report on our recent efforts to extend this nitride pyrometer technology to multiwafer MOCVD reactors. (Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.).