A method used to overcome polarization effects in semi-polar structures of nitride light-emitting diodes emitting green radiation

Abstract

Polarization effects are studied within nitride light-emitting diodes (LEDs) manufactured on standard polar and semipolar substrates. A new theoretical approach, somewhat different than standard ones, is proposed to this end. It is well known that when regular polar GaN substrates are used, strong piezoelectric and spontaneous polarizations create built-in electric fields leading to the quantumconfined Stark effects (QCSEs). These effects may be completely avoided in nonpolar crystallographic orientations, but then there are problems with manufacturing InGaN layers of relatively high Indium contents necessary for the green emission. Hence, a procedure leading to partly overcoming these polarization problems in semi-polar LEDs emitting green radiation is proposed. The (1122) crystallographic substrate orientation (inclination angle of 58 • to c plane) seems to be the most promising because it is characterized by low Miller-Bravais indices leading to highquality and high Indium content smooth growth planes. Besides, it makes possible an increased Indium incorporation efficiency and it is efficient in suppressing QCSE. The In 0.3 Ga 0.7 N/GaN QW LED grown on the semipolar (1122) substrate has been found as currently the optimal LED structure emitting green radiation.

Study of nanostructures and interfaces of technological materials by means of electron microscopy techniques

“…However, in other sites of the sample, steps of 1-2 atomic planes are observed, as shown in the next HRTEM image (Fig. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. It is clearly observed that in this case, after CMP process, the 4H-SiC surface is smooth, but some few regions with more than four Si-C bilayers step height still exist.…”

“…As already mentioned, the strain analysis (Fig. [6][7][8][9][10][11][12][13][14][15][16][17][18][19] showed the existence of several stressed areas on the SiC/AlN interface. These areas are connected with the presence of some steps on the SiC surface.…”

“…However, in this case, the amorphous layer was observed at some regions at a depth of about 13nm in the Si substrate as well (Fig. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. The insets in this figure represent the FFT transform of the areas indicated by white colored arrows denoting the Si areas surrounding the amorphous layer.…”

“…Polarization induces tilted energy bands in polar nitrides, favor of the formation of a highdensity 2DEG (2-Dimensional Electron Gas) in electronic devices [15]. However, in other electronic devices such as LEDs (Light-Emitting Diodes), the polarization effects create builtin electric fields resulting to quantum-confined Stark effects (QCSEs) [18]. The spontaneous polarization Psp of the group III-nitrides was calculated by F. Bernardini and V. Fiorentini [19]: -0.081 (C/m 2 ) for AlN, -0.029 (C/m 2 ) for GaN and finally -0.032 (C/m 2 ) for InN, as shown in detail in Fig.…”

“…As in the "on axis" situation, in the 4 deg cut off case a thin amorphous interlayer probably SiNx, was revealed by HRTEM at the AlN-1/Si substrate interface (Fig. [5][6][7][8][9][10][11][12][13][14][15][16][17][18], as also mentioned in the work of Kaiser et al [93]. Similarly to the previous sample, the layers' thickness is not homogeneous in all areas, varying from around 1 up to 2nm.…”