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19 pages, 5864 KB

Open AccessArticle

Modeling Lattice Matched Dilute Nitride Triple and Quadruple Junction Solar Cells on Virtual SiGe Substrate

by Tugba S. Navruz

Photonics 2023, 10(6), 630; https://doi.org/10.3390/photonics10060630 - 30 May 2023

Viewed by 1999

A lattice matched triple junction solar cell (TJSC) structure with a GaAs_0.58 P_0.42 top cell and bandgap tunable GaN_xAs_1-x-zP_z middle and bottom cells on virtual SiGe substrate is proposed in this study. SiGe/Si substrate is preferred as it is a low-cost substrate and because it provides a lattice constant at which bandgap tunable dilute nitride materials that are appropriate for highly efficient multijunction solar cells can be obtained. By changing the nitrogen content in GaN_xAs_1-x-zP_z, the bandgap of the middle and bottom subcells is adjusted to the optimum values. The bandgap of the top cell is constant at 1.95 eV. Three models with different values of surface recombination velocities and Shockley–Read–Hall recombination lifetimes are applied to the presented TJSC structure. Peak efficiencies of 48.9%, 40.6% and 33.7% are achieved at E_G2 = 1.45 eV and E_G3 = 1.04 eV for Model 1, E_G2 = 1.45 eV and E_G3 = 1.15 eV for Model 2, and E_G2 = 1.5 eV and E_G3 = 1.17 eV for Model 3, respectively. A fourth bandgap adjustable GaN_xAs_1-x-zP_z junction is inserted into the system and a significant improvement is obtained under high sun concentration for Models 1 and 2. The presented original results are very promising because the variable bandgaps provide very efficient absorption of incoming spectrum. Full article

(This article belongs to the Topic Photovoltaic Materials and Devices)

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15 pages, 4936 KB

Open AccessArticle

Monolithic Integration of O-Band InAs Quantum Dot Lasers with Engineered GaAs Virtual Substrate Based on Silicon

by Buqing Xu, Guilei Wang, Yong Du, Yuanhao Miao, Ben Li, Xuewei Zhao, Hongxiao Lin, Jiahan Yu, Jiale Su, Yan Dong, Tianchun Ye and Henry H. Radamson

Nanomaterials 2022, 12(15), 2704; https://doi.org/10.3390/nano12152704 - 5 Aug 2022

Cited by 24 | Viewed by 3906

Abstract

The realization of high-performance Si-based III-V quantum-dot (QD) lasers has long attracted extensive interest in optoelectronic circuits. This manuscript presents InAs/GaAs QD lasers integrated on an advanced GaAs virtual substrate. The GaAs layer was originally grown on Ge as another virtual substrate on Si wafer. No patterned substrate or sophisticated superlattice defect-filtering layer was involved. Thanks to the improved quality of the comprehensively modified GaAs crystal with low defect density, the room temperature emission wavelength of this laser was allocated at 1320 nm, with a threshold current density of 24.4 A/cm⁻² per layer and a maximum single-facet output power reaching 153 mW at 10 °C. The maximum operation temperature reaches 80 °C. This work provides a feasible and promising proposal for the integration of an efficient O-band laser with a standard Si platform in the near future. Full article

(This article belongs to the Special Issue Silicon-Based Nanostructures: Fabrication and Characterization)

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13 pages, 5385 KB

Open AccessArticle

Dual-Step Selective Homoepitaxy of Ge with Low Defect Density and Modulated Strain Based on Optimized Ge/Si Virtual Substrate

by Buqing Xu, Yong Du, Guilei Wang, Wenjuan Xiong, Zhenzhen Kong, Xuewei Zhao, Yuanhao Miao, Yijie Wang, Hongxiao Lin, Jiale Su, Ben Li, Yuanyuan Wu and Henry H. Radamson

Materials 2022, 15(10), 3594; https://doi.org/10.3390/ma15103594 - 18 May 2022

Cited by 8 | Viewed by 2827

Abstract

In this manuscript, a novel dual-step selective epitaxy growth (SEG) of Ge was proposed to significantly decrease the defect density and to create fully strained relaxed Ge on a Si substrate. With the single-step SEG of Ge, the threading defect density (TDD) was successfully decreased from 2.9 × 10⁷ cm⁻² in a globally grown Ge layer to 3.2 × 10⁵ cm⁻² for a single-step SEG and to 2.84 × 10⁵ cm⁻² for the dual-step SEG of the Ge layer. This means that by introducing a single SEG step, the defect density could be reduced by two orders of magnitude, but this reduction could be further decreased by only 11.3% by introducing the second SEG step. The final root mean square (RMS) of the surface roughness was 0.64 nm. The strain has also been modulated along the cross-section of the sample. Tensile strain appears in the first global Ge layer, compressive strain in the single-step Ge layer and fully strain relaxation in the dual-step Ge layer. The material characterization was locally performed at different points by high resolution transmission electron microscopy, while it was globally performed by high resolution X-ray diffraction and photoluminescence. Full article

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13 pages, 7238 KB

Open AccessArticle

Growth of GaP Layers on Si Substrates in a Standard MOVPE Reactor for Multijunction Solar Cells

by Pablo Caño, Carmen M. Ruiz, Amalia Navarro, Beatriz Galiana, Iván García and Ignacio Rey-Stolle

Coatings 2021, 11(4), 398; https://doi.org/10.3390/coatings11040398 - 30 Mar 2021

Cited by 9 | Viewed by 3653

Abstract

Gallium phosphide (GaP) is an ideal candidate to implement a III-V nucleation layer on a silicon substrate. The optimization of this nucleation has been pursued for decades, since it can form a virtual substrate to grow monolithically III-V devices. In this work we present a GaP nucleation approach using a standard MOVPE reactor with regular precursors. This design simplifies the epitaxial growth in comparison to other routines reported, making the manufacturing process converge to an industrial scale. In short, our approach intends to mimic what is done to grow multijunction solar cells on Ge by MOVPE, namely, to develop a growth process that uses a single reactor to manufacture the complete III-V structure, at common MOVPE process temperatures, using conventional precursors. Here, we present the different steps in such GaP nucleation routine, which include the substrate preparation, the nucleation itself and the creation of a p-n junction for a Si bottom cell. The morphological and structural measurements have been made with AFM, SEM, TEM and Raman spectroscopy. These results show a promising surface for subsequent III-V growth with limited roughness and high crystallographic quality. For its part, the electrical characterization reveals that the routine has also formed a p-n junction that can serve as bottom subcell for the multijunction solar cell. Full article

(This article belongs to the Special Issue Thin Films and Nanostructures by MOCVD: Fabrication, Characterization and Applications)

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10 pages, 4729 KB

Open AccessArticle

Room Temperature Electroluminescence from Tensile-Strained Si_0.13Ge_0.87/Ge Multiple Quantum Wells on a Ge Virtual Substrate

by Guangyang Lin, Ningli Chen, Lu Zhang, Zhiwei Huang, Wei Huang, Jianyuan Wang, Jianfang Xu, Songyan Chen and Cheng Li

Materials 2016, 9(10), 803; https://doi.org/10.3390/ma9100803 - 27 Sep 2016

Cited by 16 | Viewed by 6682

Abstract

Direct band electroluminescence (EL) from tensile-strained Si_0.13Ge_0.87/Ge multiple quantum wells (MQWs) on a Ge virtual substrate (VS) at room temperature is reported herein. Due to the competitive result of quantum confinement Stark effect and bandgap narrowing induced by tensile strain in Ge wells, electroluminescence from Γ1-HH1 transition in 12-nm Ge wells was observed at around 1550 nm. As injection current density increases, additional emission shoulders from Γ2-HH2 transition in Ge wells and Ge VS appeared at around 1300–1400 nm and 1600–1700 nm, respectively. The peak energy of EL shifted to the lower energy side superquadratically with an increase of injection current density as a result of the Joule heating effect. During the elevation of environmental temperature, EL intensity increased due to a reduction of energy between L and Γ valleys of Ge. Empirical fitting of the relationship between the integrated intensity of EL (L) and injection current density (J) with L~J^m shows that the m factor increased with injection current density, suggesting higher light emitting efficiency of the diode at larger injection current densities, which can be attributed to larger carrier occupations in the Γ valley and the heavy hole (HH) valance band at higher temperatures. Full article

(This article belongs to the Special Issue Silicon Nanophotonics)

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