Study On AlGaN Channel Material Growth And Device Fabrication With Superlattice Structure

In recent years,as the key material of UHF high-power devices GaN-based heterojunction materials have been widely studied for their structural design,fabrication,and process optimization.Increasing the power density to reduce the device size has always been a goal pursued by researchers.We use AlGaN channel heterojunction materials instead of conventional AlGaN/GaN heterojunctions to increase the operating voltage of HEMTs.During the growth of the channel material,a superlattice structure is used to increase the quality of the AlGaN channel and reduce the adverse effects of alloy scattering on the carrier mobility,so as to improve the saturation current density of the AlGaN channel material HEMTs.This article studies the growth of AlGaN channel heterojunction and device fabrication with superlattice structure and obtains the following results1.Growing Al0.73Ga0.27N/Al0.22Ga0.78N and Al0.72Ga0.28N/Al0.20Ga0.80N heterojunction,the latter has a high-Al composition AlGaN barrier with a superlattice structure.The FWHM of the?002?plane rocking curve are 354.1 arcsec and 318.5 arcsec.The FWHM of the?102?plane rocking curve are 426.4 arcsec and 405.2 arcsec,respectively.The superlattice structure improves the surface morphology of the sample,the atomic step is clearer,and the RMS decreases from 0.361 nm to 0.313 nm.The mobility of sample 2DEG increases from 739.0 cm²/V·s to 1010.2 cm²/V·s.2.Growth Al_0.72Ga_0.28N/Al_0.32Ga_0.68N heterojunction in which the channel layer is transformed into an AlN/GaN superlattice structure to reduce the alloy disorder scattering effect on electron mobility.The FWHM of the?002?plane and the?102?plane rocking curve are 487.7 and 479.2 arcsec,respectively.The surface of the sample has been improved,and the atomic steps has been refined and the RMS has been reduced from0.313 nm to 0.273 nm.The mobility of sample 2DEG increases to 1175.6 cm²/V·s,the2DEG density is 6.6×10¹² cm^-2,and the square resistance value is 808?/?.3.HEMTs are fabricated using conventional Al_xGa_1-xN/Al_yGa_1-yN heterojunction materials and superlattice AlGaN channel heterojunction materials.AlGaN channel with superlattice material Al composition is 32%,The fabricated device with superlattice has a larger breakdown voltage,and the saturation current density is almost not decreased compared to the HEMTs fabricated from the conventional AlGaN channel material.The device breakdown voltage is 368 V with the gate voltage at 5 V and the gate drain distance Lgd at8?m.The output current density is 189.6 mA/mm and the peak trans- conductance is 86.3 mS/mm.The DIBL coefficient is small at 5.6 mV/V.4.The ohmic contact TLM pattern of the device sample is tested and analyzed,and the ohmic contact resistance of the AlGaN channel material is 1.999?·mm.The high Al AlGaN barrier increases the difficulty of ohmic contact fabrication.The test results shows that the sheet resistance of the material is basically consistent with the material characterization test in Chapter 3.The Schottky contact characteristics of the device samples are tested and analyzed.It is found that the device fabricated with the traditional AlGaN channel material has a larger leakage current of 12.5×10^-6 mA/mm,and the device fabricated with the superlattice structure AlGaN channel has a lower leakage current of 8.2×10^-6 mA/mm,the crystal quality of the AlGaN channel material in the superlattice structure is good,and the gate leakage of the device is suppressed.