In a described example, an integrated circuit (IC) is disclosed that includes a transistor. The transistor includes a substrate, and a buffer structure overlying the substrate. The buffer structure has a first buffer layer, a second buffer layer overlying the first buffer layer, and a third buffer layer overlying the second buffer layer. The first buffer layer has a first carbon concentration, the second buffer layer has a second carbon concentration lower than the first carbon concentration, and the third buffer layer has a third carbon concentration higher than the second carbon concentration. An active structure overlies the buffer structure.

A method for preparing a super junction trench MOSFET, comprising: providing a substrate, and forming a first trench in the substrate; depositing an epitaxial portion of a first stage in the first trench while supplying a doped gas and an etching gas, and performing an epitaxial process after stopping supplying the doped gas and the etching gas, wherein impurities in the epitaxial portion of the first stage are diffused to an upper portion of the first trench and to form an epitaxial portion of a second stage with a gradient concentration by utilizing a high-temperature environment of the epitaxial process; forming a well region, a trench gate, and an active region in the substrate at a periphery of the first trench; forming an interlayer dielectric layer covering the column, the trench gate, and the active region; and electrically leading out the column, the trench gate, and the active region.

Embodiments according to the present invention provide a method for manufacturing a GaN HEMT power semiconductor epitaxy wafer having a high-quality, high-resistance buffer region, comprising: a first GaN buffer layer formation step in which carbon is doped using a metal-organic source among sources supplied for GaN growth as a precursor for carbon doping; and a second GaN buffer layer formation step in which carbon is doped by supplying a precursor for carbon doping separately from the sources supplied for GaN growth; wherein the precursor for carbon doping in the second GaN buffer layer formation step is at least one of CH.sub.4 (methane), C.sub.2H.sub.4 (ethylene), C.sub.2H.sub.2 (acetylene), C.sub.3H.sub.8 (propane), i-C.sub.4H.sub.10 (iso-butane), and [N(CH.sub.3).sub.3] (trimethylamine).

Embodiments of the present disclosure generally relate to epitaxial processes and materials, and more specifically, epitaxial processes for preparing materials, layers, stacks, and devices. In one or more embodiments, a device includes a multi-layer structure disposed on a substrate. The multi-layer structure includes a plurality of doped silicon-germanium (SiGe) layers. The doped SiGe layers respectively include a dopant having a concentration in a range from about 0.01 atomic percent (at%) to about 5 at%. The multi-layer structure includes a plurality of silicon layers disposed in an alternating arrangement with the doped SiGe layers such that a respective silicon layer is disposed between a respective first doped SiGe layer and a respective second doped SiGe layer.