Fikadu Alema1,Takeki Itoh2,Akhil Mauze2,James S. Speck2,Shubhra S. Pasayat3,Chirag Gupta3,Andrei Osinsky1
Agnitron Technology Incorporated1,University of California, Santa Barbara2,University of Wisconsin-Madison3
Fikadu Alema1,Takeki Itoh2,Akhil Mauze2,James S. Speck2,Shubhra S. Pasayat3,Chirag Gupta3,Andrei Osinsky1
Agnitron Technology Incorporated1,University of California, Santa Barbara2,University of Wisconsin-Madison3
β-Ga<sub>2</sub>O<sub>3</sub> has recently become the focal point of ultra-wide bandgap semiconductor research for power electronics due to its high breakdown field (~ 8 MV/cm) and the availability of high-quality native substrates. It is also receptive to multiple dopants used to control its n-type conductivity, realizing wide doping ranges from 2x10<sup>14 </sup>to >3x10<sup>20</sup> cm<sup>-3</sup> using Ge and Si impurities for films grown in an MOCVD method. On the other hand, β-(Al<sub>x</sub>Ga<sub>1-x</sub>)<sub>2</sub>O<sub>3</sub> (AlGaO) ternary alloys have been widely studied to modulate the bandgap of Ga<sub>2</sub>O<sub>3</sub>, which is crucial to design and realize power electronic devices with great flexibility. However, achieving a high doping concentration in the β-(Al<sub>x</sub>Ga<sub>1-x</sub>)<sub>2</sub>O<sub>3</sub> layers remains challenging. In this presentation, we report on the MOCVD growth of heavily doped (>10<sup>20</sup> 1/cm<sup>3</sup>) strained β-(Al<sub>x</sub>Ga<sub>1-x</sub>)<sub>2</sub>O<sub>3</sub>/β-Ga<sub>2</sub>O<sub>3</sub> layers with an Al composition of up to 25%. Triethylgallium (TEGa), triethylaluminium (TEAl), and silane were used as a source for Ga, Al, and Si and oxygen for oxidation. The layer thickness and Al content in the β-(Al<sub>x</sub>Ga<sub>1-x</sub>)<sub>2</sub>O<sub>3 </sub>films were estimated from the Omega-2Thetta XRD scans, whereas Hall measurements were utilized to determine electron mobility and free carrier concentration. β-(Al<sub>x</sub>Ga<sub>1-x</sub>)<sub>2</sub>O<sub>3</sub>/β-Ga<sub>2</sub>O<sub>3</sub> layers with free carrier concentrations ranging between 5x10<sup>16</sup> and >1x10<sup>20</sup> cm<sup>-3</sup> were demonstrated for AlGaO films with different Al content. The effects of AlGaO layer thickness and Al content in the incorporation of silicon were studied. Free carrier concentration in the AlGaO layer was found to decrease with Al content and the increase of layer thickness due to relaxation. This presentation will discuss the growth of high-quality β-(Al<sub>x</sub>Ga<sub>1-x</sub>)<sub>2</sub>O<sub>3</sub>/β-Ga<sub>2</sub>O<sub>3</sub> superlattice structure with sharp interfaces and sub-nanometer surface roughness. We will also present the realization of a modulation-doped two-dimensional electron gas (2DEG) in β-(Al<sub>0.2</sub>Ga<sub>0.8</sub>)<sub>2</sub>O<sub>3</sub>/Ga<sub>2</sub>O<sub>3</sub> heterostructure by silicon delta doping as well as demonstration of delta-doped Ga<sub>2</sub>O<sub>3</sub>/(Al<sub>x</sub>Ga<sub>1-x</sub>)<sub>2</sub>O<sub>3</sub>/Ga<sub>2</sub>O<sub>3 </sub>double heterostructures--both building blocks of lateral power field-effect transistors.