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Interface Trap Density Reduction for Al2O3/GaN (0001) Interfaces by Oxidizing Surface Preparation prior to Atomic
Dmitry M Zhernokletov1, Muhammad A Negara1, Rathnait D Long1
1†Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States.
ACS Applied Materials & Interfaces
|May 20, 2015
Summary
Investigating aluminum oxide (Al2O3) on gallium nitride (GaN) interfaces, this study reveals that NH4OH pretreatment minimizes interface defects. This chemical treatment enhances metal-oxide-semiconductor device performance by reducing trap densities.
Area of Science:
- Materials Science
- Semiconductor Physics
- Surface Chemistry
Background:
- Metal-oxide-semiconductor (MOS) structures are crucial for modern electronics.
- The Al2O3/GaN interface quality significantly impacts device performance.
- Understanding and controlling interfacial defects is key to advancing GaN-based electronics.
Purpose of the Study:
- To correlate interfacial defect state densities with the chemical composition of the Al2O3/GaN interface.
- To investigate the influence of wet chemical pretreatments (HCl+HF etching vs. NH4OH exposure) on the Al2O3/GaN interface prior to atomic layer deposition (ALD).
- To identify the optimal pretreatment for reducing interface state density in MOS capacitors on n-type GaN.
Main Methods:
- Synchrotron photoelectron emission spectroscopy (PES) to analyze surface chemical composition.
- Cathodoluminescence (CL) to assess optical properties and band edge emission.
- High-temperature capacitance-voltage (C-V) measurements to determine interface state densities.
- Atomic layer deposition (ALD) of Al2O3 on n-type GaN (0001) substrates.
Main Results:
- NH4OH(aq) exposure prior to ALD resulted in a greater Ga2O3 component on the surface compared to HCl+HF etching or as-received surfaces.
- Acid etching (HCl+HF) yielded the lowest surface oxygen concentration, while NH4OH treatment resulted in the lowest surface carbon concentration.
- Both pretreatments improved electrical characteristics by reducing interface state density compared to untreated samples.
- NH4OH pretreatment led to the lowest interfacial trap density in the upper band gap, correlating with stronger band edge emission observed via CL.
- PES indicated that NH4OH treatment reduced carbon contamination while maintaining a Ga2O3 interfacial layer, contributing to fewer interface traps.
Conclusions:
- NH4OH(aq) exposure is an effective pretreatment for Al2O3/GaN interfaces, minimizing carbon contamination and forming a beneficial Ga2O3 layer.
- This pretreatment significantly reduces interfacial trap densities, leading to improved electrical performance of MOS capacitors.
- The findings provide a pathway for optimizing GaN-based MOS device fabrication through controlled surface chemistry.
