15:15 〜 15:30
▲ [14p-502-7] Effect of Nitridation on Properties of AlN/β-Ga2O3 Composite Structures
キーワード：AlN/Ga2O3 composite structure, Nitridation
We expect that AlN/β-Ga2O3 heterostructures would produce high-density two-dimensional electron gas (2DEG) at the interface due to the spontaneous polarization in AlN. In this work, we performed heteroepitaxial growth of AlN thin films on β-Ga2O3 (-201) substrates by plasma-assisted molecular beam epitaxy (PAMBE) and studied structural and electrical properties of the AlN/Ga2O3 composite structures.
Two different samples having the same AlN(5 nm)/Ga2O3 (-201) structure were prepared by PAMBE to study effects of Ga2O3 surface nitridation on structural and electrical properties of AlN/Ga2O3 composite structures. For one sample, the Ga2O3 surface was nitrided at a substrate temperature of 300 °C prior to the AlN growth, and there was no nitridation process for the other one.Grain-type surface morphology with a root-mean-square (RMS) roughness of 1.9 nm was observed for the sample without nitridation by atomic force microscopy. On the other hand, the sample with nitridation showed smaller grains and a smoother surface with an RMS roughness of 0.8 nm, compared to the sample without nitridation.
Metal-oxide-semiconductor (MOS) capacitors were fabricated using the AlN/Ga2O3 structures for capacitance–voltage (C–V) measurement. A 20-nm-thick Al2O3 layer was formed on the AlN by atomic layer deposition to suppress leakage current. The backside Ti-based cathode electrode exhibited a good ohmic contact.
The sample without the nitridation process showed an almost constant capacitance, independent of the forward and reverse biases. However, the sample with nitridation revealed accumulation and saturation behaviors in capacitance with increasing voltage in the forward bias range and depletion followed by saturation in the reverse bias range. When compared these experimental results with simulated C–V curves for Al2O3/AlN/Ga2O3 MOS capacitors with and without 2DEG at the AlN/Ga2O3 interface (an assumed ns=7×1012 cm-2), it is clear that 2DEG is absent at AlN/Ga2O3 interface for both samples.
This work was partially supported by Grants-in-Aid for Scientific Research No. 25289093 from MEXT, Japan.
Two different samples having the same AlN(5 nm)/Ga2O3 (-201) structure were prepared by PAMBE to study effects of Ga2O3 surface nitridation on structural and electrical properties of AlN/Ga2O3 composite structures. For one sample, the Ga2O3 surface was nitrided at a substrate temperature of 300 °C prior to the AlN growth, and there was no nitridation process for the other one.Grain-type surface morphology with a root-mean-square (RMS) roughness of 1.9 nm was observed for the sample without nitridation by atomic force microscopy. On the other hand, the sample with nitridation showed smaller grains and a smoother surface with an RMS roughness of 0.8 nm, compared to the sample without nitridation.
Metal-oxide-semiconductor (MOS) capacitors were fabricated using the AlN/Ga2O3 structures for capacitance–voltage (C–V) measurement. A 20-nm-thick Al2O3 layer was formed on the AlN by atomic layer deposition to suppress leakage current. The backside Ti-based cathode electrode exhibited a good ohmic contact.
The sample without the nitridation process showed an almost constant capacitance, independent of the forward and reverse biases. However, the sample with nitridation revealed accumulation and saturation behaviors in capacitance with increasing voltage in the forward bias range and depletion followed by saturation in the reverse bias range. When compared these experimental results with simulated C–V curves for Al2O3/AlN/Ga2O3 MOS capacitors with and without 2DEG at the AlN/Ga2O3 interface (an assumed ns=7×1012 cm-2), it is clear that 2DEG is absent at AlN/Ga2O3 interface for both samples.
This work was partially supported by Grants-in-Aid for Scientific Research No. 25289093 from MEXT, Japan.