Photovoltaic action from InxGa1-xN p-n junctions with x > 0.2 grown on silicon (original) (raw)
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Design, growth, fabrication and characterization of high-band gap InGaN/GaN solar cells
2006
One of the key requirements to achieve solar conversion efficiencies greater than 50% is a photovoltaic device with a band gap of 2.4 eV or greater. InxGa1-xN is one of a few alloys that can meet this key requirement. InGaN with indium compositions varying from 0 to 40% is grown by both metal-organic, chemical-vapor deposition (MOCVD) and molecular beam epitaxy (MBE), and studied for suitability in photovoltaic applications.
Design and Realization of Wide-Band-Gap ($\sim$2.67 eV) InGaN p-n Junction Solar Cell
IEEE Electron Device Letters, 2010
The design of coherently strained InGaN epilayers for use in InGaN p-n junction solar cells is presented in this letter. The X-ray diffraction of the epitaxially grown device structure indicates two InGaN epilayers with indium compositions of 14.8% and 16.8%, which are confirmed by photoluminescence peaks observed at 2.72 and 2.67 eV, respectively. An open-circuit voltage of 1.73 V and a short-circuit current density of 0.91 mA/cm 2 are observed under concentrated AM 0 illumination from the fabricated solar cell. The photovoltaic response from the InGaN p-n junction is confirmed by using an ultraviolet filter. The solar cell performance is shown to be related to the crystalline defects in the device structure. Index Terms-Fabrication, InGaN solar cell, solar cell. I. INTRODUCTION W IDE-BAND-GAP (> 2.4 eV) materials are required in multiple-junction solar cells to achieve ultrahigh (> 50%) efficiency [1]. InGaN alloy is one of the few materials with band gap > 2.4 eV, and the band gap range of this alloy is tunable from 0.65 to 3.4 eV. III-nitride materials are direct band gap semiconductors and have strong absorption coefficients of ∼10 5 cm −1 at the band edge while simultaneously possessing other desirable characteristics such as radiation hardness and high peak and saturation velocities [2], [3]. InGaN solar cells with record high open-circuit voltage of 2.0 V [4] and high internal quantum efficiency [5], [6] have been demonstrated. These results were achieved with InGaN/GaN doubleheterojunction p-in structures with intrinsic InGaN layers. The InGaN composition in these devices was < 12%.
Acta Materialia, 2013
We report a comparison of the morphological, structural and optical properties of both InGaN single-layer and multilayered structures, the latter consisting of periodic thin GaN interlayers inserted during InGaN growth. It is shown that such a structure suppresses the In concentration fluctuations and corresponding different states of strain relaxation with depth, both detrimental to solar cell applications. Measurements performed by X-ray diffraction, cathodoluminescence and photoluminescence demonstrate that this multilayer growth is a promising approach to increase both the InGaN layer total thickness and In content in InGaN epilayers. As an example, single-phase 120 nm thick InGaN with 14.3% In content is obtained and found to possess high structural quality.
Nearly similar molar ratio of In and Ga in indium gallium nitride (InGaN)/Si photocells prefers to match InGaN conduction level energy to Si valance energy band for ohmic contact between two cells. At high temperature fabrication process, InGaN-Si interface shows highly defecting prone. Considering those tussles, InGaN-based/Si-based double-junction tandem solar cell was designed and fabricated. In 0.4 Ga 0.6 N cell was fabricated on Si photocell by implementing AlN/SiO 2 /Si 3 N 4 interlayers. Interlayer influence on quantum efficiency of InGaN cell was studied under ideal irradiance AM1.5 solar spectrum at 300°K. Because of insertion of interlayers between InGaN and Si; the gradual efficiency enhancement with respect to the overlayer h-GaN (a = 3.183 nm) plane lattice was found to 8.3%, 5.9% and 5.1% for AlN (a = 3.11 nm), for SiO 2 (a = 4.9 nm) and for Si 3 N 4 (a = 7.76 nm), respectively. AlN was found to be an excellent and SiO 2 as preferable interlayer compared with Si 3 N 4. Coherence (in-plane lattice matching) of nano-interlayer appears to reduce photonic electro-migration hurdle between InGaN and Si; therefore, progressive enrichment of efficiency was realized.
MOVPE Growth of InxGa1−xN (x ∼ 0.4) and Fabrication of Homo-junction Solar Cells
Journal of Materials Science & Technology, 2013
The metal organic vapor phase epitaxy (MOVPE) growth of indium gallium nitride (InGaN) has been discussed in detail towards the fabrication of solar cell. The InGaN film with In contents up to 0.4 are successfully grown by controlling the fundamental growth parameters such as the precursor gas flow rates, temperature etc. The formation of metallic In originates from the higher value (0.74) of trimethylindium/ (trimethylindium þ triethylgallium) (TMI/(TMI þ TEG)) molar ratio with low (4100) V/III weight molar ratio while the lower value (0.2) of TMI/(TMI þ TEG) causes the phase separation. It is also necessary to control the growth rate and epitaxial film thickness to suppress the phase separation in the material. The crystalline quality of grown films is studied and it is found to be markedly deteriorated with increasing In content. The lattice parameters as well as the thermal expansion coefficient mismatch between GaN template and InGaN epi-layer are primarily considered as the reasons to deteriorate the film quality for higher In content. By using In 0.16 Ga 0.84 N films, an n þ ep homo-junction structure is fabricated on 0.65 mm GaN template. For such a device, the response to the light illumination (AM 1.5) is observed with an open circuit voltage of 1.4 V and the short circuit current density of 0.25 mA/cm 2. To improve the performance as well as increase solar photon capturing, the device is further fabricated on thick GaN template with higher In content. The In 0.25 Ga 0.75 N n þ ep junction solar cell is found better performance with an open circuit voltage of 1.5 V and the short circuit current density of 0.5 mA/cm 2. This is the InGaN pen homo-junction solar cell with the highest In content ever reported by MOVPE.
Energy Science & Engineering
Solar cells of ternary alloys such as indium gallium nitride (InGaN) are attracting interest due to the tunable direct band gap energy of InGaN covering the whole solar spectrum ranging from 0.7 eV (band gap energy of InN) to 3.4 eV (band gap energy of GaN), 1,2 as well as superior photovoltaic characteristics of InGaN including high absorption coefficients (~10 5 cm −1) 3 and high carrier mobility. 1 Moreover, high stability (thermal and chemical) and superior radiation resistance of InGaN alloys allow operation of InGaN-based devices in extreme conditions such as space and terrestrial applications. 1,4 InGaN-based solar cells have been successfully fabricated with low indium contents of the InGaN alloy. 5-7 Lower indium content in InGaN leads to an increase in the band gap energy of InGaN, which in turn results in