Spatial Inhomogeneity of Photoluminescence in an InGaN-Based Light-Emitting Diode Structure Probed by Near-Field optical Microscopy Under Illumination-Collection Mode

Abstract

Spatial distribution of photoluminescence (PL) spectra has been assessed in an InGaN single quantum well (SQW)-based light-emitting diode structure by near-field optical microscopy under the illumination-collection mode. The obtained PL mapping image revealed a variation in both peak and intensity of PL spectra according to the probing location with a scale less than about 200 nm. The variation in PL intensity is from 0.8 to 1.8 in arbitrary units indicating that the internal quantum efficiency fluctuates from 10% to 50% within the active layer.

Confocal microphotoluminescence of InGaN-based light-emitting diodes

“…4͑b͔͒ of the yellow-green LED was not so clear. We have already reported the similar behavior of yellow-green LED probed by the SNOM measurement 23 and confocal microscopy. 26 In this case, the areas of long PL wavelength ͑small PL peak energy͒ correspond to indiumrich areas.…”

“…[20][21][22] Quite recently, our group succeeded in obtaining the highly resolved PL images by using the SNOM with illumination-collection mode. 23,24 In this method, both excitation and detection were operated through the same optical fiber tip. The similar highly resolved PL image is obtainable by using the confocal microscopy, while the experimental setup and operation are much easier.…”

“…Recently, a cathodoluminescence [17][18][19] ͑CL͒ or a scanning near-field optical microscopy [20][21][22][23][24][25] ͑SNOM͒ has been used as a powerful alternative method to obtain optical images of InGaN / GaN in a submicrometer scale. However, spatial resolutions of CL and SNOM are still limited by the diffusion lengths of carriers.…”

Near-field scanning optical microscopic transient lens for carrier dynamics study in InGaN∕GaN

“…The spatial inhomogeneity of NSOM-PL is well known and interpreted to be the inhomogeneity of indium composition by the phase separation. [3][4][5][6][7][8][9][10][11][12][13][14][15][16] The bright regions correspond to the high density region of the carrier localization centers, which act as the radiative recombination centers ͑RCs͒. On the other hand, the spatial inhomogeneity of NSOM-TL should denote the carrier distribution in the InGaN active layer because we already knew that the NSOM-TL signal is attributed to only the ␦N ͓Fig.…”

“…1,2 In order to improve the efficiency of light emission from InGaN QW, we have to elucidate and understand the carrier dynamics and light emission mechanics. There are a lot of reports on the spatial resolved studies for InGaN by cathodoluminescence, [3][4][5] near-field scanning optical microscopy ͑NSOM͒, [6][7][8][9][10][11][12] or scanning confocal microscopy. 13,14 By these techniques, the radiative carrier recombination process has been observed with submicrometer scale.…”