Properties of selective area growth patterns for gallium-nitride selfseparation in hydride vapor phase epitaxy Martin Klein1,*, Robert Leute1,2, Tobias Meisch1, Frank Lipski1,3, Ferdinand Scholz1 1 Institute of Optoelectronics, University of Ulm, Albert-Einstein-Allee 45, 89081 Ulm, Germany 2 Now with: Automotive Lighting Reutlingen GmbH, Tübinger Str. 123, 72762 Reutlingen, Germany 3 Now with: Robert Bosch GmbH, Tübinger Str. 123, 72762 Reutlingen, Germany *Email:
[email protected] In order to achieve the best possible performance in the field of gallium-nitride (GaN) high power lasers and transistors, it is necessary to base the production of such devices on native GaN substrates. GaN substrates available today are based on a variety of fabrication techniques, such as ammonothermal growth, GaN boule growth in hydride vapor phase epitaxy (HVPE) and the natrium-flux method, with each method having its distinct advantages and disadvantages. Our approach is concentrating on producing single freestanding GaN layers in HVPE, on metal organic vapor phase (MOVPE) grown templates. The separation of the resulting GaN layer from the template is achieved through a self-separation mechanism during the cool down phase, after the growth of the thick GaN layer. In order to have a better control of the separation step, we have developed an ex-situ interlayer that is acting as a predetermined breaking point[1]. Although this method showed promising results from the first experiments on, cracking of the resulting wafers has been an issue ever since. Variations in the filling factors and optimization of the overgrowth procedure could partly improve the situation and has lead to the fabrication of layers, that separated in one piece from the underlying template. Unfortunately these layers still contained overgrown cracks, that reached from the sample surface to the wafer backside. Recently we started adapting a mask pattern design, where the bowing behaviour of the wafer during growth and cool down phase is taken into account. By varying the filling factor from the wafer center to the wafer edge, we are able to greatly reduce the amount of visible cracks, up to the point, that the sample backside is totally crack free.
Fig. 1: Wafer Frontside
Fig. 2: Wafer Backside
[1] F. Lipski, T. Wunderer, S. Schwaiger, and F. Scholz, Phys. Status Solidi A, 207, 1287 (2010).
