Nitrogen diffusion in the Si growth on GaN by low-pressure chemical vapor deposition
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Si film has been grown on a wurtzite gallium nitride layer on sapphire by low-pressure chemical vapor deposition. Uniform nitrogen incorporation was found in the Si film at the concentration of 5%, indicating an incorporation-limited process through interstitial diffusion from GaN layer to Si layer. The nitrogen occupied the substitutional sites in the Si film, leading this Si layer to be n-type doping with the carrier concentration of 1.42 × 1018/cm3 and the hall mobility of 158 cm2/(V s). This is consistent with other calculated and experimental results, which suggest that only 5% nitrogen can occupy the substitutional sites in the nitrogen-doped Si materials.
GaN and related materials have a great potential for use in optical and electronic devices. To combine the advantages for both GaN and Si materials together, GaN growth on a Si substrate has been intensively studied by molecular beam epitaxy, metalorganic chemical vapor deposition, and hydride vapor phase epitaxy.1–7 However, high-quality GaN materials are difficult to grow due to the large mismatch on the lattice constant and thermal coefficient. The other concern is the Si incorporation into the growth GaN materials, which degrades the material quality. On the other hand, Ga and N species will react with Si substrate to distort the structure of the buried Si materials during the GaN growth process. It is therefore interesting and important to study the reaction mechanism between Ga and N with Si materials to grow GaN materials in a controlled way. The other way to make complex GaN/Si devices is to grow low-temperature Si films on the GaN materials. In contrast to the case of GaN growth on a Si substrate, few experiments on Si films grown on GaN have been reported. There is one report claiming the deposition of Si by rf sputtering on GaN can improve its ohmic contact,8 which is ascribed to the Si diffusion into the GaN films and then the formation of highly doped n+-type GaN layers. In this case, the specific contact resistivity decreased as the annealing temperature increased.8 To the best of our knowledge, no other papers have discussed trying to grow Si layers on GaN materials. The study of Si growth on GaN will also provide useful information
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Address all correspondence to this author. e-mail: [email protected] b) e-mail: [email protected] J. Mater. Res., Vol. 17, No. 8, Aug 2002
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into the reaction mechanism of Ga and N with Si materials, and a better Si/GaN interface may be obtained due to the low growth temperatures. Such a better interface may be beneficial to fabricate some interesting devices such as multiwavelength detectors. In this work, we will report Si layer growth on GaN materials on a sapphire substrate by low-pressure chemical vapor deposition (LPCVD). A uniform 5% N atom incorporation in the Si films indicates an incorporationlimited process through interstitial diffusion from the GaN layer to the Si layer. The Si films were grown in a hot-wall LPCVD system. The reactor was made
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