2005 Fiscal Year Final Research Report Summary
Electron microscopy analysis by visualization of relationship between composition distribution and charge distribution in quantum well of GaN system
| Project/Area Number |
16560287
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (C)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
Electronic materials/Electric materials
|
|---|
| Research Institution | National Institute for Materials Science |
|---|
Principal Investigator |
TAKEGUCHI Masaki National Institute for Materials Science, High-voltage electron microscopy station, Senior Researcher, 超高圧電子顕微鏡ステーション, 主任研究員 (30354327)
|
|---|
| Project Period (FY) |
2004 – 2005
|
| Keywords | Electron holography / Z-contrast STEM / Transmission electron microscopy / Quantum well structure / Charge density distribution / Interface abruptness |
|---|
| Research Abstract |
Piezo electric field of InGaN layer in InGaN/GaN quantum well structure was measured by electron holography. This piezo electric field was caused by lattice strain along c-axis in InGaN layer. We calculated lattice constant from In composition according to Vegards law, and then estimated piezo-polarization. We prepared some samples with various thickness from one wafer. Electron holography was carried out for those samples and internal electric field value evaluated was 0.7±0.2 MV/cm. This value corresponds to the In composition 4.1±1.3% estimated from the theoretical calculation. On the other hand, Z-contrast STEM observation allowed us to evaluate the In composition 4.8±1.6%, which agree to the value obtained by electron holography.
As for AlGaN/GaN quantum well structure, we established the sample preparation technique, e.g., Samples were thinned by wedge-polishing method followed by Ar-ion milling with low voltage, so that the sample thickness was 50-100 nm. This thickness was enough thin to be observed by HRTEM and Z-contrast STEM, and electron holography. From these comprehensive studies, it was found that piezo electric field of AlGaN in AlGaN/GaN quantum well is considerably small rather than InGaN in InGaN/GaN quantum well, suggesting that minimization of damage layer on the sample surfaces and precise thickness measurement are indispensable.
|
