Linear thermal expansion coefficient determination using in situ curvature and temperature dependent X-ray diffraction measurements applied to metalorganic vapor phase epitaxy-grown AlGaAs

AlxGa1xAs grown on GaAs is known to be almost perfectly lattice matched with a maximum lattice mismatch of 0.14% at room temperature and even less at temperatures of 700 C–800 C. However, as layer structures for edge-emitting diode lasers exhibit an increasing overall thickness of several microns of AlxGa1xAs, e.g., diode lasers comprising a super-large optical cavity, the accumulated elastic strain energy increases as well. Depending on the growth temperature the formation energy of dislocations can be reached, which is limiting the pseudomorphic growth. In this regard, the thermal expansion coefficient difference between layer and substrate is an important parameter. We utilize in situ curvature measurements during growth of AlxGa1xAs by metal-organic vapour phase epitaxy to determine the thermal expansion coefficient a. The curvature change with increasing layer thickness, as well as with wafer temperature at constant layer thickness is used to assess a. This is compared to ex situ temperature dependent X-ray diffraction measurements to obtain a. All determined values for α are in good agreement, yielding αAlAs = 4.1×10−6 K−1 for a given GaAs linear thermal expansion coefficient of αGaAs = 5.73×10−6 K−1.