The authors present optical and electrical data for long wavelength (573–601nm) InGaN∕GaN multiple quantum well light emitting diodes (LEDs) grown by metal organic chemical vapor deposition. These results are achieved by optimizing the active layer growth temperature and the quantum well width. Also, the p-GaN is grown at low temperature to avoid the disintegration of the InGaN quantum wells with high InN content. A redshift is observed for both the green and yellow LEDs upon decreasing the injection current at low current regime. In the case of the yellow LED, this shift is enough to push emission into the amber (601nm).

As such, metal contacts play an important role for thin-film thermoelectric (TE) devices, especially in high heat-flux applications (e.g., chip cooling) where low contact resistivity (ρ C ) is critical to device performance. [15][16][17] Recent work [18] has demonstrated low electrical contact resistivity ρ C in the range 1-2 × 10 −6 Ω cm 2 in TE modules based on (Bi,Sb) 2 Te 3 superlattices using the evaporation of Cr/Ni/ Au to fabricate metal electrodes. For thinfilm thermoelectric modules with the TE thickness <2 µm, further reduction of ρ C to 10 −8 Ω cm 2 is needed for the contact resistivity to be a small fraction of the resistivity of the thermoelectric element itself. [18] Creating such low contact resistivities is challenging from a fabrication perspective, [19] but also because little is known about the fundamental properties of metal contacts to these materials. For example, even basic properties such as the atomic and electronic structure of the metal/TE interface are largely unknown. This makes it difficult to optimize the contact resistivity and to establish the fundamental limits [20] that are possible. To address this challenge, we present an integrated theoretical and experimental effort toward understanding the limits of low-ρ C in realistic metal contacts to advanced TE materials. We present a new multiscale theoretical approach combining ab initio calculations and continuum mesoscopic models to investigate the structural, electronic, and transport properties of electrical contacts to novel TE materials used in thin-film, superlattice V-telluride devices. We show that the nature of these semiconductor materials leads to unusual contact properties, such as strong n-type doping near the interface and interfacial atomic dipoles that completely determine the band bending. We predict that significant improvement over previously reported experimental data is possible, and we present new experimental data that demonstrate a 100-fold reduction in contact resistivity. Detailed atomistic spatially resolved measurements of the new contacts show that additional improvement should be possible. Importantly, we demonstrate that the reduction in contact resistivity can be harnessed to improve the thermoelectric efficiency of cooling modules.To understand the electrical properties of contacts to (Bi,Sb) 2 Te 3 materials and their realistic low ρ C limit we carried out a series of large scale ab initio calculations of the Sb 2 Te 3 -Cr V-telluride superlattice thin films have shown promising performance for on-chip cooling devices. Recent experimental studies have indicated that device performance is limited by the metal/semiconductor electrical contacts. One challenge in realizing a low resistivity contact is the absence of fundamental knowledge of the physical and chemical properties of interfaces between metal and V-telluride materials. This study presents a combination of experimental and theoretical efforts to understand, design, and harness low resistivity contacts to V-tellurides. Ab initio calculations a...

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