Channeling defects in group-III nitrides during dry etching processes
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Channeling defects in group-III nitrides during dry etching processes O. Breitschädel, J.T. Hsieh, B. Kuhn, F. Scholz, and H.Schweizer 4. Phys. Institute, University of Stuttgart, Pfaffenwaldring 57, D-70550 Stuttgart, Germany Phone: +49-711-685-4961, Fax: +49-711-685-5097, [email protected] ABSTRACT The effects of Ar+ ion beam etching (IBE) of AlGaN/GaN heterostructures and GaN/InGaN/GaN quantum well structures were investigated dependent on different ion incidence angles. The AlGaN/GaN heterostructure was measured before and after etching with respect to mobility and sheet resistance. The InGaN quantum well structure was measured with PL to determine the PL intensity and the energy shift, respectively. This experiments show that ion channeling is a significant defect generation phenomena in groupIII nitrides at vertical ion incidence angle and can be minimized by tilting the sample against the ion beam. INTRODUCTION The nitride semiconductors are very promising with respect to a large number of applications, because of their large band gap, their high thermal conductivity, and their chemical inertness. Thus, this material has a large potential for the fabrication of optoelectronic devices like light emitting diodes in a wide wavelength range from red to blue and injection lasers operating in the blue to UV [1], as well as electronic devices operating under extremely harsh conditions [2]. Up to now much is known about group-III nitride semiconductor compounds, but considerable further work is required in the area of process technology. One important part of processing devices based on GaN is the dry etching step, because group-III nitrides are chemically inert in all acids and bases at room temperature. Dry etching is a widely used tool in semiconductor fabrication like mesa formation in electrical devices or mirror etching in laser diodes. Many dry-etching methods are developed like reactive ion etching [3], ion beam etching [4], and chemically assisted ion beam etching [5] (reactive ion beam etching). One potential disadvantage when using dry etching technique is the introduction of etching defects. The primary mechanism for defect creation deep in the crystal is ion channeling, i.e., the scattering of ions along low-index directions of the crystallattice. Most Monte Carlo simulation techniques like TRIM [6] assume no crystalline structure and thus don’t take into account this effect. The range distribution of channeled ions can be higher than a factor of 2 – 50 compared to TRIM calculated ranges even at low energies between 50 to 150 keV [7]. The study of channeled ions can offer information about the channeling mechanism but from the device processing’s point of view the aim should be to avoid channeling. In this work we want to show, that ion channeling during dry-etching is one of the most important defect generation mechanisms even at low energies. Two sets of experiments were performed, one in AlGaN/GaN heterostructures used as an electrical proof, the second one in GaN/InGaN quantum w
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