Twist's Review #2 - Interesting Interaction between Oxides

Paper : Scalable and highly tunable conductive oxide interfaces

This paper described a process for making tunable conductive oxide interfaces, here demonstrated with two oxides which are SrTiO3 and Al2O3. The conductive area itself is called a 2-Dimensional Electron Gas or 2DEG, which is essentially a group of electrons aligned in a 2 dimensional geometry. While 2DEGs has been previously observed before in another material system, particularly the LaAlO3 (LAO) and SrTiO3 (STO), these were usually made epitaxiall using Pulse Laser Deposition (PLD). Now while PLD results in great quality and precision, is quite slow and expensive thus not limiting its scalability. This paper aims to try and solve that problem.

In this paper they used Al2O3/STO, created using Atomic Layer Deposition (ALD), a well-known deposition method, due to its higher potential for scalability. Asides from that, the group also offers tunability to the conductivity of the oxide interface by doing a pretreatment using NH3 plasma in the ALD chamber, where the time for pretreatment is the tuning parameter, without change to the structure and smoothness of the interface.

Pretreatment was done from 30 seconds - 4 minutes and it was found that the oxide interace exhibits a metal-insulator transition (MIT), where at 30 - 40 seconds it behaves as an insulator and at 50 seconds and above it behaves as a metal. This was found through the measurements they did (I think it is through their magnetoresistance and Hall measurements). Now the numbers show that there is up to a six orders of magnitude of increase/decrease depending on the pretreatment time, which can be observed in particular at 50K where the resistance is about 10^7 with 30 seconds of pretreatment and about 1 with 4 minutes of pretreatment. This tunability is possible due to a reduction process happening at the STO interface due to the NH3 pretreament, creating oxygen vacancies and increasing the charge density.

[1] Cohen-Azarzar, Dana, Maria Baskin, Andreas Lindblad, Felix Trier, and Lior Kornblum. “Scalable and Highly Tunable Conductive Oxide Interfaces.” APL Materials 11, no. 11 (November 17, 2023): 111118. Scalable and highly tunable conductive oxide interfaces | APL Materials | AIP Publishing.

So this paper is not directly related to semiconductors, but the application may be related to devices such as trasistors and memory due to this 2DEG. I thought this paper was interesting because of two things, the materials mentioned included perovskites and the fact that 2DEGs form between oxides. 2DEGs, as some may already know, are used in GaN devices, in particular GaN-based High-Electron-Mobility Transistor (HEMT) which I think is why the device is called a HEMT in the first place. Through this paper, I have truly realized the versatility of perovskites, which I guess is also due to its “flexibility” with regard to its crystal structure. I wonder what other applications perovskites may be used for…?

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