Dualtronics: Double-Sided Epitaxial Integration of III-Nitride Devices on GaN Substrates

The GaN material system offers a wide range of applications, including light emitters covering a broad spectral range from visible to ultraviolet light, as well as high-power and radio-frequency transistors. A crucial material property of III-nitrides utilized in heterostructure design is the built-in polarization. Since GaN primarily crystallizes in the wurtzite structure, which breaks inversion symmetry along the c-axis [0001], opposite surfaces along this direction exhibit drastically different physical and electronic properties. This fact can be leveraged for specific applications. However, since polarization is dictated by the substrate polarity, until now, the use of a single wafer implied only one alignment of polarization in the devices grown on top of it.

In this work, we propose leveraging the unique advantages of the GaN material system, its wide range of applications, and the support of high-quality bulk substrates to develop a new method for monolithic integration of electronic and optoelectronic devices on the same wafer. By utilizing consecutive epitaxial growth processes on both polarities of GaN substrates, i.e., the gallium face (0001) and nitrogen face (000-1), it is possible to achieve structures with distinct physical and chemical properties on the same bulk crystal. We demonstrate the ability to control epitaxial growth on both polarities of GaN by plasma-assisted molecular beam epitaxy, presenting the monolithic integration of a metal-polar light-emitting diode (LED) and a nitrogen-polar high electron mobility transistor (HEMT) [1], as well as double-sided LEDs emitting at distinct wavelengths. The obtained integrated structures can pave the way for new device functionalities.
[1] L. van Deurzen, E. Kim, et al., Nature, 634 (2024) 334.