External Article: Another Step Towards Oxide based Optronics

Background

III-V semiconductors are the preferred choice for RF, Power and space/ defense applications. Though expensive, they offer many advantages over silicon like higher power handling capacity, break down voltage etc.

Fig.1 Typical HEMT structure with 2DEG at AlGaN/GaN interface[1]

We are familiar with the concept of two-dimensional electron gas(2DEG) in III-V semiconductors which form the basis of High Electron Mobility Transistor(HEMT).

The 2DEG is created due to a triangular quantum well formation at the heterojunction(between semiconductor materials) causing quantum confinement[3][4].

Fig.2 Typical HEMT structure with 2DE G at AlGaN/GaN interface[2]

As ionized impurities are absent(to induce electrons), the scattering is minimal, leading to higher mobility(hence current) versus Si-based devices.The electron density in case of III-Nitride 2DEG is about ∼5 × 10¹³ cm⁻².

In 2004, the turf of III-V semiconductors was challenged when researchers found the presence of high-density 2DEG at an oxide interface(LaAlO₃ & SrTiO₃) which exceeded the values seen in III-Nitride 2DEG[5][6]. Similarly, GdTiO₃-SrTiO₃ heterostructure grown on an oxide substrate has demonstrated 2DEG electron density >3 × 10¹⁴ cm⁻² [5][7]. Devices based on these oxides have the potential of being used as sensors, Field Effect Transistors(FETs) etc.

Fig.3 Band diagram of STO-LAO interface with 2DEG[6][11]

The only hindrance to realizing the full potential of oxides for Optronics application is the current use of single crystal oxide substrates for material/film growth[5].

For commercial viability, we would like to use single crystal substrates like silicon(001) or (111) with some demonstrations already being made for adoption[8][9][10]

• LTO-STO heterostructure on Si(100) with a 2DEG charge density of 8.9 × 10¹⁴ cm⁻²
• GdTiO₃-SrTiO₃ on Si(001) with a 2DEG charge density of ∼9 × 10¹³ cm⁻²

Taking another step in this direction, researchers at Yale University have added a new substrate for the growth of oxides – GaAs(III-V material)[5]. They have been able to grow GdTiO₃-SrTiO₃ heterostructure on GaAs wafer using MBE. The electron density obtained at the GTO–STO interface is ∼2 × 10¹⁴ cm⁻² [5].

Article

https://publishing.aip.org/publishing/journal-highlights/new-oxide-and-semiconductor-combination-build-new-devices

Further Reading

L. Kornblum et. al.,”Oxide heterostructures for high-density 2D electron gases on GaAs”, Journal of Applied Physics,123,025302,2018

In the future, post optimization and scaling, the devices fabricated on these films can act as the baseline for the next-generation electronic and optical devices.

If you want to share your opinion kindly do so in the comments section or email me at u2d2tech@gmail.com.

References:

1. http://www.semiconductor-today.com/news_items/2010/APRIL/UCSB_150410.htm
2. M. Aadit et. al, “High Electron Mobility Transistors: Performance Analysis, Research Trend and Applications, Different Types of Field-Effect Transistors – Theory and Applications”, InTech, 10.5772/67796, 2017
3. https://en.wikipedia.org/wiki/Two-dimensional_electron_gas
4. http://uef.fei.stuba.sk/moodle/mod/book/view.php?id=7920&chapterid=63
5. L. Kornblum et. al.,”Oxide heterostructures for high-density 2D electron gases on GaAs”, Journal of Applied Physics,123,025302,2018
6. A. Ohtomo et. al.,”A high-mobility electron gas at the LaAlO₃/SrTiO₃ heterointerface”, Nature volume427, pages423–426, 29 January 2004

7. P.Moetakef et. al.,”Transport in ferromagnetic GdTiO3/SrTiO3 heterostructures”, Appl. Phys. Lett. 98, 112110, 2011

8. E. Jin et.al.,”A high density two-dimensional electron gas in an oxide heterostructure on Si (001)”, APL Materials 2, 116109, 2014

9. L. Kornblum et. al.”Oxide 2D electron gases as a route for high carrier densities on (001) Si”, Appl. Phys. Lett. 106, 201602,2015
10. L. Kornblum et. al. “Electronic transport of titanate heterostructures and their potential as channels on (001) Si”, Journal of Applied Physics 118, 105301, 2015
11. https://en.wikipedia.org/wiki/Lanthanum_aluminate-strontium_titanate_interface

12. U. Treske et. al., “Universal electronic structure of polar oxide heterointerfaces”, Scientific Reports volume5, Article number: 14506, 2015

13. M Lorenz et al,”The 2016 oxide electronic materials and oxide interfaces roadmap”, Physics D: Applied Physics 49,43,2016
14. J.H. Yoon et. al, “Electronic Band Alignment at Complex Oxide Interfaces Measured by Scanning Photocurrent Microscopy”, Scientific Reports 7, Article number: 3824 (2017)
15. https://www.synchrotron-soleil.fr/en/news/universal-fabrication-two-dimensional-electron-gases-functional-oxides-future-applications

16. Changjian Li et. al, “Tailoring the Two Dimensional Electron Gas at Polar ABO₃/SrTiO₃ Interfaces for Oxide Electronics”, Scientific Reports 5, Article number: 13314 (2015)

17. https://www2.physics.ox.ac.uk/research/oxide-electronics