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Correlative High‐Resolution Mapping of Strain and Charge Density in a Strained Piezoelectric Multilayer

2014; Wiley; Volume: 2; Issue: 1 Linguagem: Inglês

10.1002/admi.201400281

2196-7350

Kyung Song, Christoph T. Koch, Ja Kyung Lee, Dong Yeong Kim, Jong Kyu Kim, Amin Parvizi, Woo Young Jung, Chan Gyung Park, Hyeok Jae Jeong, Hyoung Seop Kim, Ye Cao, Tiannan Yang, Long‐Qing Chen, Sang Ho Oh,

ZnO doping and properties

A key to strain engineering of piezoelectric semiconductor devices is the quantitative assessment of the strain‐charge relationship. This is particularly demanding in current InGaN/GaN‐based light‐emitting diode (LED) designs as piezoelectric effects are known to degrade the device performance. Using the state‐of‐the‐art inline electron holography, we have obtained fully quantitative maps of the two‐dimensional strain tensor and total charge density in conventional blue LEDs and correlated these with sub‐nanometer spatial resolution. We show that the In 0.15 Ga 0.85 N quantum wells are compressively strained and elongated along the polar growth direction, exerting compressive stress/strain on the GaN quantum barriers. Interface sheet charges arising from a polarization gradient are obtained directly from the strain data and compared with the total charge density map, quantitatively verifying only 60% of the polarization charges are screened by electrons, leaving a substantial piezoelectric field in each In 0.15 Ga 0.85 N quantum well. The demonstrated capability of inline electron holography provides a technical breakthrough for future strain engineering of piezoelectric optoelectronic devices.