GaAs/Ge tandem-cell space concentrator development

Wojtczuk, S.; Tobin, S. P.; Keavney, C.J.; Bajgar, C.; Sanfacon, M.M.; Geoffroy, L.M.; Dixon, T.M.; Vernon, S. M.; Scofield, James D.; Ruby, D.S.

doi:10.1109/16.46383

Cited by 39 publications

(9 citation statements)

References 13 publications

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“…Heterogeneous integration of Ge and GaAs has attracted much attention due to their promising applications in optoelectronic devices such as solar cells and dual band optical sensors because of the expanded spectral coverage [1][2][3][4][5]. The negligible distinction in the lattice constants and thermal expansion coefficients of Ge and GaAs poses convenience for this heterogeneous integration.…”

Section: Introductionmentioning

confidence: 99%

P-type Ge epitaxy on GaAs (100) substrate grown by MOCVD

Jin

Chia

Liu

et al. 2016

Applied Surface Science

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Section: Introductionmentioning

confidence: 99%

P-type Ge epitaxy on GaAs (100) substrate grown by MOCVD

Jin

Chia

Liu

et al. 2016

Applied Surface Science

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“…It shows a considerable advantage over other TI systems including graphene [3], HgTe QW, [4,5] the Bi chalcogenides [9] and the Heusler compounds [12,17]. GaAs/Ge/GaAs sandwiched structures are readily to be integrated with conventional semiconductors which are already extensively used in electronic devices [23][24][25][26][27][28][29][30][31]. The imposed electric field can be controlled by applying extra electric field or by inducing holes or electrons into the QW region via a gate voltage, providing us a direct way of manipulating the TI transition in the device.…”

mentioning

confidence: 99%

“…[23][24][25][26] Ge/GaAs interfaces with exceedingly small lattice mismatch posses many advantages over the strained interface. Ge layers grown on GaAs substrate were studied because of their widespread applications in solar cells, [27] metal-oxide-semiconductor field-effect transistors, [28] millimeter-wave mixer diodes, [29] temperature sensors, [30] and photodetectors. [31] Considering a GaAs/Ge/GaAs quantum well (QW) grown along the polar direction [111] (see Fig.…”

mentioning

confidence: 99%

Interface-Induced Topological Insulator Transition inGaAs/Ge/GaAsQuantum Wells

Zhang¹,

Lou²,

Miao³

et al. 2013

Phys. Rev. Lett.

134

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We demonstrate theoretically that interface engineering can drive Germanium, one of the most commonly-used semiconductors, into topological insulating phase. Utilizing giant electric fields generated by charge accumulation at GaAs/Ge/GaAs opposite semiconductor interfaces and band folding, the new design can reduce the sizable gap in Ge and induce large spin-orbit interaction, which lead to a topological insulator transition. Our work provides a new method on realizing TI in commonly-used semiconductors and suggests a promising approach to integrate it in well developed semiconductor electronic devices.PACS numbers: 71.70. Ej, 75.76.+j, 72.25.Mk Time-reversal invariant topological insulators (TIs) have aroused intensive interests in the past years, with tantalizing properties such as insulating bulk, robust metallic edge or surface modes and exotic topological excitations, and potential applications ranging from spintronics to quantum computation. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Despite these successful progresses, the topological insulator materials are still limited in the narrow gap materials containing heavy atoms, e.g., HgTe, [4,5] Bi 2 X 3 (X=Se, Te,...) [8][9][10][11], transition metal oxide heterostructure [16] and Heusler compounds [12,17]. These materials are often very different from conventional semiconductor materials in structures and properties and are hard to be integrated in current electronics devices that are based on well developed semiconductor fabrication technologies.Although there are theoretical predicts about realizing TI states in graphene, [3,18,19] the main obstacle is the weak intrinsic spin-orbit interaction (SOI) of carbon atoms. Here, instead of searching new TI materials with exotic structures and chemical elements, we take a totally different route: driving the commonly used semiconductors into TI states by using the intrinsic electric field and the strains. The difficulty of this approach lies in the fact that most of the commonly used semiconductors, such as Si, Ge, GaAs and many others usually possess sizable band gaps and do not have strong enough SOI. Furthermore, group IV elements such as Si and Ge have indirect band gap, posing extra difficulty in realizing TI. Inspired by recent theoretical works that the normal insulator [20] can be driven into a TI by an external electric field, our approach is to impose huge electric field by deliberately designed heterostructures. Recently, an interesting way of realizing topological insulating phase in a p-type GaAs quantum well by two-dimentional superimposed potentials with hexagonal symmetry was proposed.[21] Different to that work, our approach rely completely on the material engineering at the atomic level.Since commonly-used semiconductors, e.g., Si, Ge, GaAs, posses sizable bandgap ranging from 0.8eV to 1.4eV, a huge electric field is required to closing bandgap and even invert the conduction and valence bands. Such huge electric field can not be generated utilizing the gate technique. However, recent ...

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“…The cell is very similar to standard high efficiency PIN GaAs space cells [4]. The exception is the inclusion of a high aluminum composition etch stop layer buried at the back of the cell, as well as heavily doped back contact region needed for an alloyless (low temperature) contact to the N GaAs back surface after the GaAs wafer and AlGaAs etch stop are removed.…”

Section: Mil Coverglass [3] Astropower Cell Efficiency Is Similar Tomentioning

confidence: 97%

High-power density (1040 W/kg) GaAs cells for ultralight aircraft

Wojtczuk

Reinhardt²

1996

Conference Record of the Twenty Fifth IEEE Photovoltaic Specialists Conference - 1996

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Ultralight 5 pm thick P/N GaAs solar cells were bonded to 3 mil coverglass with 1 mil of adhesive to create very high power density cellsfor use in ultralight aircraft. Cells were first made on a thick GaAs wafer and then bonded to a coverglass. The GaAs wafer was removed by selectively etching through the wafer to a buried etch stop in the cell epilayers. The cell was completed with a final non-alloyed back metal contact to prevent heat damage to the adhesive, as opposed to a high temperature alloyed contact used in a normal thick P/N GaAs cell. Prototype 1x1 cm cells were measured by microbalance at an average weight of 0.0228 g/cm2 with a one-sun AM0 efficiency up to 17.3% at 28 C (VOC 1.024V, Jsc 29.9 mA/cm2, FF 77.4%) for a cell power density of 1040 W/kg (weight including coverglass, adhesive and cell). Table I compares power densities of lightweight silicon (Si) and GaAs cells on germanium (Ge) wafers with the ultralight GaAs cells described here assuming the same 1 mil of GE RTV615 adhesive between the cell and the 3 mil coverglass for all technologies. Table 1 Comparison for cell technology power density . 18%GaAs 15% 17% on 8 mil Ge 4 mil Si 5p GaAs I 3milcover(kg/mz) I 0.175 I 0.175 I 0.175 I 1 mil GE RTV(kg/mz) I 0.026 I 0.026 I 0.026 OVERVIEW I Total Weight (kg/m2) 1 1.261 I 0.431 1 0.228Flying-wing ultralight unmanned aerial vehicles (UAVs), similar to the RAPTOR Pathfinder, may soon be used in military reconnaissance or environmental ozone layer monitoring. These aircraft may eventually use very lightweight, high-power-density solar arrays on the wings as the main power source during the day. The solar alrrays power the aircraft and charge batteries or other energy storage devices to be used at night. In one type of mission, the aircraft would reach its maximum altitude during the day (when maximum sun power is available) and then fall to a somewhat lower altitude at night, when it is running from its secondary power source, before returning to its maximum altitude the next day again. Altitudes and missions are affected by the power densrty (powerheight factor) of the solar arrays in use, as well as battery energy densrty, and a host of other factors.This report describes ultralight, thin P/N GaAs cells epitaxially grown by metal organic chemical vapor deposition (MOCVD) and fabricated by Spire such that a thin 3 mil Pilkington GaAs-thermal-expansion-matched 3 mil CMG coverglass was used as the final support substrate. These cells are unlike conventional high-efficiency Ill-V solar cells in that the inactive substrate wafer was removed after the cell was bonded to the coverglass. The wafer contributes 97% of the weight and thickness of a conventional cell (5 pm) on an 8 mil (200pm) wafer. Although the weight reduction becomes less dramatic after the weight of the coverglass, adhesive and backing material or superstrate are factored in, it is still substantial. 49 0-7803-3166-4/96/$5.00 0 1996 EEE

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GaAs/Ge tandem-cell space concentrator development

Cited by 39 publications

References 13 publications

P-type Ge epitaxy on GaAs (100) substrate grown by MOCVD

P-type Ge epitaxy on GaAs (100) substrate grown by MOCVD

Interface-Induced Topological Insulator Transition inGaAs/Ge/GaAsQuantum Wells

High-power density (1040 W/kg) GaAs cells for ultralight aircraft

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