Regrowth method for fabricating wide-bandgap transistors, and devices made thereby
| DWPI Title: Method for fabricating high electron mobility transistor, involves regrowing nitride contact material regrown with graded composition that initially matches channel layer composition but progressively decreases in bandgap |
| Abstract: Methods are provided for fabricating a HEMT (high-electron-mobility transistor) that involve sequential epitaxial growth of III-nitride channel and barrier layers, followed by epitaxial regrowth of further III-nitride material through a window in a mask layer. In examples, the regrowth takes place over exposed portions of the channel layer in the source and drain regions of the device, and the regrown material has a composition different from the barrier layer. In other examples, the regrowth takes place on the barrier layer, only in the access region or regions. Devices made according to the disclosed methods are also provided. |
| Use: Method for fabricating high electron mobility transistor (HEMT) for use in radio-frequency electronics and power switching applications. |
| Advantage: The aluminum gallium nitride (AlGaN)/aluminum nitride (AlN) HEMT can be successfully fabricated and tested with an aluminum content in the channel layer as high as 85% by using the regrowth technique to add GaN beneath the source and drain contact metal. The access-region resistivity in HEMTs can be reduced by using the method for regrowing semiconductor material over the barrier layer in the access regions. The epitaxial regrowth process assures that the graded AlGaN grows only in the source and drain contact region and not on top of the protective mask. The voids can be selectively etched out in the barrier layer in the source and drain regions. The aluminum coefficient in the channel layer is increased in order to drive up the breakdown voltage and to increase the lateral figure of merit (LFOM). |
| Novelty: The method involves epitaxially growing a III-nitride channel layer on a substrate. A III-nitride barrier layer is epitaxially grown on the channel layer. A dielectric mask layer is deposited on the barrier layer. A window is opened through the dielectric mask layer in a source region and in a drain region. The etching (304) is done through the source region window and through the drain region window so as to remove barrier layer material and a void is left in the barrier layer which is reaching down to an exposed upper surface of the channel layer. The voids in the source and drain regions are filled by epitaxial regrowth of the III-nitride contact material that differs in composition from the barrier layer. The III-nitride contact material is regrown with a graded composition that initially matches the channel layer composition but progressively decreases in bandgap during the regrowth. |
| Filed: 3/14/2018 |
| Application Number: US15921007A |
| Tech ID: SD 14049.1 |
| This invention was made with Government support under Contract No. DE-NA0003525 awarded by the United States Department of Energy/National Nuclear Security Administration. The Government has certain rights in the invention. |
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