台大光电所所讯

Spatial Range of the Plasmonic Dicke Effect in an InGaN/GaN Multiple Quantum Well Structure

Professor C. C. Yang’s Lab.

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

台湾大学光电所杨志忠教授

The plasmonic Dicke effect means a cooperative emission mechanism of multiple light emitters when they are simultaneously coupled with the same surface plasmon (SP) mode of a metal nanostructure to achieve a higher collective emission efficiency. Here, we compare the enhancements of emission efficiency among a series of SP-coupled InGaN/GaN quantum-well (QW) structures of different QW period numbers to show an emission behavior consistent with the plasmonic Dicke effect. The relative enhancement of overall emission efficiency increases with QW period number until it reaches a critical value, beyond which the enhancement starts to decrease. This critical QW period number corresponds to the effective depth range of the plasmonic Dicke effect in a multiple-QW system. It also represents an optimized QW structure for maximizing the SP coupling effect. Internal quantum efficiency (IQE) and time-resolved photoluminescence are measured for comparing the enhanced emission efficiencies of blue and green QW structures with different QW period numbers through SP coupling induced by surface Ag nanoparticles. Figure 1 below shows the structures of the 5 single-QW samples of different capping layer thicknesses and the 6 QW samples of different QW period numbers. Figure 2 shows the transmission spectra of those samples after Ag nanoparticles are placed on the top. The depressions correspond to the SP resonance feature. Figures 3 and 4 show the IQEs of those samples and their relative enhancements.

Fig. 1 (a): Structure of the 5 single-QW samples with different d. (b): Structure of the 6 QW samples with 1-6 QW period numbers.

Fig. 2 Transmission spectra of the totally 11 samples shown in Fig. 1. The insert shows the SEM image of the Ag nanoparticles on the sample top to produce SP coupling.

Fig. 3 Variations of the IQEs of the 5 single-QW samples and their relative enhancements.

Fig. 4 Variations of the IQEs of the 6 QW samples of different QW numbers and their relative enhancements.

In_0.53Ga_0.47As/InP SAGCM avalanche photodetectors

Professor Hao-Hsiung Lin’s Lab.

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

台湾大学光电所林浩雄教授

In this work, we report on the design and fabrication of In_0.53Ga_0.47As/InP avalanche photodetectors (APDs) with separated absorption, grading, charge sheet, and multiplication (SAGCM) structure. We used TCAD model to simulate 2D APD device structures with guard rings. The designed structures were realized on InP substrates by MOCVD growth and twice Zn diffusion processes. The depth of junction, thickness of the multiplication layer, and the depth of guard ring were controlled by the two diffusions. Fig. 1 shows the schematic diagram of the device structure and the fabricated APD devices. Fig. 2 shows the revise I-V of an APD in dark and under the illumination of a 1550 nm light source. Fitting results are also shown in the figure. Fig. 4 shows the measured external quantum efficiency of an APD with and without gain.

Fig. 1(a) Schematic diagrams showing the device structure and the electric field profile. (b) Microscope image showing APD devices.

Fig. 2 Reverse dark and illuminated I-V curves of the APD devices. The 1550 nm light source induces the current jump at the punch through voltages. Fitting results from TCAD are also shown in the figure.

Fig. 3 External quantum efficiency of an APD device with gain (M_pη) and without gain (η).