Mr. Weihua Zhang Profile

Weihua Zhang

at Peking Univ

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Publications (1)

Proceedings Article | 9 February 2005 Paper

High spatial resolution investigation of electroluminescence of InGaN/GaN multiple quantum wells by using scanning near-field optical microscopy and spectroscopy

Weihua Zhang, Gengzhao Xu, Xing Zhu

Proceedings Volume 5635, (2005) https://doi.org/10.1117/12.570641

KEYWORDS: Near field scanning optical microscopy, Electroluminescence, Light emitting diodes, Indium, Quantum wells, Indium gallium nitride, Gallium nitride, Spatial resolution, Spectroscopy, Green light emitting diodes

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The electro-luminescence (EL) properties of InGaN/GaN multiple quantum wells (MQWs) light emitting diodes (LEDs) with various emitting wavelength (purple, blue and green) were studied by scanning near-field optical microscope (SNOM). The high spatial resolution EL SNOM mappings and near-field spectra of the LEDs were acquired at various injection current conditions. The experiment shows that, though there are some common points, the EL properties of various LEDs are quite different. (i) The EL mappings show that the MQWs emission is spatially inhomogenous, which contain many islands like bright spots. (ii) The sizes of the bright spots are different ranging from 0.1 μm to 1μm, the LED with longer emitting wavelength has larger bright spots. (iii) The injection current dependences of the shape of the bright spots of various LEDs are different. (iv) The emission wavelengths of brighter spots are longer in the same LED. (v) Increasing the injection current, the full widths at half maximum (FWHM) of the EL spectra grow larger. With the same injection current, the green LED has larger FWHMs than the blue and purple ones. (vi) Increasing the injection current, the blue shift of the green LED is obviously (~60 meV), but those of the blue one and purple are negligible. The phenomena above suggest that, the self-organized In-rich regions play a key role in the emission of all the InGaN/GaN MQWs LEDs, though they have different influences on the emission properties of the three LEDs with various emission wavelengths. One possible explanation is that, in the blue and purple LEDs, because the size of the In-rich areas are small, the quantum confined Stark effect caused by the piezoelectric field is negligible; but in the green LED, the In-rich areas are larger, the quantum confined Stark effect is obvious which caused the blue shift phenomenon. And in all LEDs, the band filling effect makes the FWHMs of the emission spectra larger. The results also show that SNOM is a powerful tool to study the local light emission properties at nanometer scale.

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