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This work is a study relating device performance and carrier escape sequence in a large set of InAsP∕InP p-i-n multi-quantum-well solar cells. The devices encompass nearly identical i-region thickness and built-in electric field and present similar absorption threshold energies. The escape sequence of the first confined electron-to-conduction band continuum and heavy/light holes-to-valence band continuum is extracted from the photoluminescence versus temperature analysis and by comparing the measured activation energies to calculated hole/electron well depths and thermionic escape times. Light holes, as expected for most III-V nanostructure systems, are found to be the fastest escaping carriers in all samples. The escape of electrons prior to heavy holes is shown to be a prerequisite to prevent severe open circuit voltage degradation. A possible explanation of the origin of this effect is offered. InP∕InAsP multi-quantum-well solar cells with high built-in electric field and fast electronic escape time display better open circuit voltage and performance.

The collection efficiency of carrier photogenerated in the intrinsic region of strained InAsxP1−x/InP multiquantum well p-i-n structures is analyzed. The existence of a critical threshold built-in electric field value above which total carrier collection becomes possible is demonstrated. Maximized carrier collection and high output voltage are systematically reached for built-in electric field exceeding the critical value while similar structures operating with a substantially lower built-in electric field (e.g., identical well characteristics but thicker i region) yields nonoptimized collection of carrier in this area and altered voltage output. The slight dependence of the critical electric field with the carrier confinement level is revealed, stressing out the importance of thermally activated escape energy. Finally, the results are discussed in the context of photovoltaic devices showing substantial efficiency improvement for devices designed with built-in electric fields in excess of the threshold value.

PACS 72.20.Jv, 72.40.+w, 84.60.Jt Standard InGaP-GaAs-Ge cell is modified by incorporating pseudomorphic multi-quantum wells (MQW) of InGaAs to increase the photocurrent of the limiting GaAs subcell. The approach as demonstrated here enables the multijunction device to be made with all sub-cells optimized, rather than with a deliberately degraded top cell, as is now the case. A modelling of the performance of the proposed device indicates possibilities for achieving practical efficiencies in excess of 35 percent under typical space sunlight illumination. The current/voltage and spectral quantum efficiency characteristics of GaAs MQW solar cells grown by chemical beam epitaxy are found to be consistent with model predictions, showing both an increase of the cell operating wavelength range and a superior current output. The device is predicted as being capable to achieve end of life efficiency of about 30 percent at radiation doses equivalent of 10 years operation in Geo-stationary orbits (1 MeV electron radiation fluences in excess of 10 15 cm -2 ). The projected radiation tolerance of the proposed device exceed significantly those of the existing conventional space solar cell technologies, making it particularly suitable for use in long duration space missions.

An eight-band Kane Hamiltonian modified for the strain has been used to describe the electronic states of the highly strained zincblende GaAs1−xNx. Conduction and valence band offsets of GaAs1−xNx with respect to InAs on InP(111) have also been investigated for different nitrogen (N) concentrations. A critical concentration of N is found, which marks the onset of type-I to type-II band alignment for GaAs1−xNx/InAs on InP(111). The effect of nitrogen on the conduction band of GaAs1−xNx has been described by the band anticrossing model. The strain balanced InAs /GaAs1−xNx short period superlattice on InP is predicted to reach operating wavelengths beyond .