InGaP/GaAs dual-junction solar cells with different tunnel diodes (TDs) grown on misoriented GaAs substrates are investigated. It is demonstrated that the solar cells with P þþ-AlGaAs/N þþ-GaAs TDs grown on 10 off GaAs substrates not only show a higher external quantum efficiency (EQE) but also generate a higher peak current density (J peak) at higher concentration ratios (185Â) than the solar cells with P þþ-GaAs/ N þþ-InGaP TDs grown on 6 off GaAs substrates. Furthermore, the cell design with P þþ-AlGaAs/N þþ-GaAs TDs grown on 10 off GaAs substrates does not generate a disordered InGaP epitaxial layer during material growth, and thus shows superior current-voltage characteristics.

A 6-dimensional grand unified theory with the compact space having the topology of a real projective plane, i.e., a 2-sphere with opposite points identified, is considered. The space is locally flat except for two conical singularities where the curvature is concentrated. One supersymmetry is preserved in the effective 4d theory. The unified gauge symmetry, for example SU(5) , is broken only by the non-trivial global topology. In contrast to the Hosotani mechanism, no adjoint Wilson-line modulus associated with this breaking appears. Since, locally, SU(5) remains a good symmetry everywhere, no UV-sensitive threshold corrections arise and SU(5)-violating local operators are forbidden. Doublettriplet splitting can be addressed in the context of a 6d N = 2 super Yang-Mills theory with gauge group SU(6). If this symmetry is first broken to SU(5) at a fixed point and then further reduced to the standard model group in the above non-local way, the two light Higgs doublets of the MSSM are predicted by the group-theoretical and geometrical structure of the model.

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In this study, we have fabricated and characterized an In 0:6 Ga 0:4 As metamorphic high-electron-mobility transistor (mHEMT) device packaged using flip-chip-on-board (FCOB) technology. A low-cost polymer substrate was adopted as the carrier for cost-effective purposes. The impact of bonding temperature on the device performance was also experimentally investigated. While the DC performance was not as sensitive, serious degradation in RF performance was observed at high bonding temperature. Such degradation was mainly due to the thermal-mechanical stress resulting from the mismatch in the coefficient of thermal expansion (CTE) between the GaAs chip and the polymer substrate. Quantitative assessment was also performed through equivalent circuit extraction from S-parameter measurements.

A discrete low noise In 0.6 Ga 0.4 As MHEMT device with 150 nm gate length was flip-chip assembled on the low-cost RO3210 organic substrate for wireless communication applications. The measured DC characteristics were very similar before and after flip-chip assembly. The flip-chip packaged MHEMT device showed a high drain current density of 516 mA/mm and a maximum transconductance of 576 mS/mm at a V DS of 0.8 V. The insertion gain of the flip-chip packaged device was decayed less than 2 dB up to 100 GHz as compared to the data of bare die. Moreover, the measured minimum noise figure was less than 2 dB as measured at V DS of 0.7 V and V GS of -0.7 V in the frequency range from 20 to 64 GHz for the device after flip-chip assembly. The excellent performance of the flip-chip packaged MHEMT device demonstrates the feasibility of using low cost organic substrate for high frequency applications up to W band.