TECHNOLOGY FOCUS - ELECTRONICS - Preferred Structure: In the solar cell structure, the active region further comprises: a hole extraction region having a valence band and a conduction band; and an electron extraction region having a valence band and a conduction band; where the absorbing region is formed between the hole extraction region and the electron extraction region, the one or more intermediate bands are thermally isolated from the valence and conduction band in the absorbing region as well as from the conduction band in the hole and electron extraction regions, the intermediate bands are partially populated by free carriers, and the conduction band offset between the absorbing region and electron extraction region and the valence band offset between the absorbing region and hole extraction region are sufficiently small to permit easy transport of carriers across these interfaces. It further comprises an upper confining region formed over the absorbing region. The intermediate band in the absorbing region is lower in energy than the conduction band in the electron extraction region, and the difference in energies of the two bands is greater than about 0.0768 eV. The intermediate band in the absorbing region is lower in energy than the conduction band in the electron extraction region, and the difference in energies of the two bands is greater than about 0.3072 eV. The intermediate band in the absorbing region is lower in energy than the conduction band in the electron extraction region, and the difference in energies of the two bands is greater than about 0.4608 eV. The intermediate band in the absorbing region is lower in energy than the conduction band in the hole extraction region, and the difference in energies of the two bands is greater than about 0.0768 eV. The intermediate band in the absorbing region is lower in energy than the conduction band in the hole extraction region, and the difference in energies of the two bands is greater than about 0.3072 eV. The intermediate band in the absorbing region is lower in energy than the conduction band in the hole extraction region, and the difference in energies of the two bands is greater than about 0.4608 eV. The conduction band of the absorbing region is lower in energy than the conduction band of the electron extraction region, and the difference in energies of the two bands is less than about 0.1536 eV. The conduction band of the absorbing region is lower in energy than the conduction band of the electron extraction region, and the difference in energies of the two bands is less than about 0.0768 eV. The conduction band of the absorbing region is about the same or higher in energy than the conduction band of the electron extraction region. The valence band of the absorbing region is higher in energy than the valence band of the hole extraction region, and the difference in energies of the two bands is less than about 0.1536 eV. The valence band of the absorbing region is higher in energy than the valence band of the hole extraction region, and the difference in energies of the two bands is less than about 0.0768 eV. The valence band in the absorbing region is about the same or higher in energy than the valence band in the hole extraction region. The dislocation density within the absorbing region is less than about 1x108 cm-2. The dislocation density within the absorbing region is less than about 1x107 cm-2. The dislocation density within the absorbing region is less than about 1x106 cm-2. It further comprises a substrate over which the solar cell structure is formed. It further comprises a buffer region, where the buffer region is formed over the substrate and a remaining solar cell structure is formed over the buffer region. The hole extraction region is the buffer region. It further comprises a back electrical contact formed on a side of the substrate opposite the hole extraction region and a front electrical contact formed over the electron extraction region on a side of the device opposite the substrate. The substrate comprises a n-type substrate, the hole electron extraction region comprises an n-type hole extraction region and the electron extraction region comprises a p-type electron extraction region. The absorbing region comprises a dilute nitride semiconductor region comprising AlnInmGa1-n-mNcAsvSbkP1-c-v-k where 0 less than or equal to n, m, v, k less than or equal to 1 and 0.001 not less than c not less than 0.2. The bandgap between an intermediate band of the absorbing region and either the valence band or the conduction band of the absorbing region is in the range of about 1.3 eV to about 1.6 eV and an overall bandgap of the absorbing region is in the range of about 2.2 eV to about 2.5 eV. The bandgap between an intermediate band of the absorbing region and either the valence band or the conduction band of the absorbing region is in the range of about 1.4 eV to about 1.5 eV and an overall bandgap of the absorbing region is in the range of about 2.3 eV to about 2.4 eV. The substrate comprises n-type callium phosphide (GaP), the hole extraction region comprises n-type GaAsxP1-x where 0.35 not less than x not less than 0.6, the absorbing region comprises n-type GaAsxNcP1-x-c where 0.005 not less than c not less than 0.2, and 0.37 not less than x not less than 0.77 and the electron extraction region comprises p-type GaP. The substrate comprises n-type GaP, the hole extraction region comprises n-type GaAsxP1-x where 0.4 not less than x not less than 0.54, the absorbing region comprises n-type GaAsxNcP1-x-c where 0.015 not less than c not less than 0.05 and 0.47 not less than x not less than 0.67 and the electron extraction region comprises p-type GaP. Alternatively, the solar cell structure comprises: a dilute nitride absorbing region located between a hole extraction region and an electron extraction region, where a bandgap between an intermediate band of the absorbing region and either the valence band or the conduction band of the absorbing region is in the range of about 1.3 eV to about 1.6 eV; an overall bandgap of the absorbing region is in the range of about 2.2 eV to about 2.5 eV; the bandgap between the conduction band in the absorbing region and the conduction band in the electron extraction region is less than about 0.1536 eV; and the bandgap between the valence band in the absorbing region and the valence band in the hole extraction region is less than about 0.1536 eV. The dilute nitride absorbing layer comprises GaAsxNcP1-x-c where 0.005 not less than c not less than 0.2, and 0.37 not less than x not less than 0.77; a bandgap between an intermediate band of the absorbing region and either the valence band or the conduction band of the absorbing region is in the range of about 1.4 eV to about 1.5 eV; an overall bandgap of the absorbing region is in the range of about 2.3 eV to about 2.4 eV; and the solar cell has a theoretical efficiency of greater than 55%. Preferred Method: Fabricating a solar cell structure further comprises: epitaxially growing a hole extraction region; and epitaxially growing an electron extraction region; where the absorbing region is epitaxially grown between the hole extraction region and the electron extraction region, the one or more intermediate bands of the absorbing region are thermally isolated from the valence and conduction band in the absorbing region as well as from the conduction band in the hole and electron extraction regions, the intermediate bands are partially populated by free carriers, and the conduction band offset between the absorbing region and electron extraction region and the valence band offset between the absorbing region and hole extraction region are sufficiently small to permit easy transport of carriers across these interfaces. It further comprises forming a back electrical contact on a side of the substrate opposite the hole extraction region; and forming a front electrical contact over the electron extraction region on a side of the device opposite the substrate. The intermediate band in the absorbing region is lower in energy than the conduction band in the electron extraction region, and the difference in energies of the two bands is greater than about 0.0768 eV. The intermediate band in the absorbing region is lower in energy than the conduction band in the electron extraction region, and the difference in energies of the two bands is greater than about 0.3072 eV. The intermediate band in the absorbing region is lower in energy than the conduction band in the electron extraction region, and the difference in energies of the two bands is greater than about 0.4608 eV. The intermediate band in the absorbing region is lower in energy than the conduction band in the hole extraction region, and the difference in energies of the two bands is greater than about 0.0768 eV. The intermediate band in the absorbing region is lower in energy than the conduction band in the hole extraction region, and the difference in energies of the two bands is greater than about 0.3072 eV. The intermediate band in the absorbing region is lower in energy than the conduction band in the hole extraction region, and the difference in energies of the two bands is greater than about 0.4608 eV. The conduction band of the absorbing region is lower in energy than the conduction band of the electron extraction region, and the difference in energies of the two bands is less than about 0.1536 eV. The conduction band of the absorbing region is lower in energy than the conduction band of the electron extraction region, and the difference in energies of the two bands is less than about 0.0768 eV. The conduction band of the absorbing region is about the same or higher in energy than the conduction band of the electron extraction region. The valence band of the absorbing region is higher in energy than the valence band of the hole extraction region, and the difference in energies of the two bands is less than about 0.1536 eV. The valence band of the absorbing region is higher in energy than the valence band of the hole extraction region, and the difference in energies of the two bands is less than about 0.0768 eV. The valence band in the absorbing region is about the same or higher in energy than the valence band in the hole extraction region. The dislocation density within the absorbing region is less than about 1x108 cm-2. The dislocation density within the absorbing region is less than about 1x107 cm-2. The dislocation density within the absorbing region is less than about 1x106 cm-2. It further comprises epitaxially growing a buffer region, where the buffer region is formed over the substrate and a remaining solar cell structure is formed over the buffer region. The substrate comprises a n-type substrate, the hole electron extraction region comprises an n-type hole extraction region and the electron extraction region comprises a p-type electron extraction region. The absorbing region comprises a dilute nitride semiconductor region comprising AlnInmGa1-n-mNcAsvSbkP1-c-v-k where 0 less than or equal to n, m, v, k less than or equal to 1 and 0.001 not less than c not less than 0.2. The bandgap between an intermediate band of the absorbing region and either the valence band or the conduction band of the absorbing region is in the range of about 1.3 eV to about 1.6 eV and an overall bandgap of the absorbing region is in the range of about 2.2 eV to about 2.5 eV. The bandgap between an intermediate band of the absorbing region and either the valence band or the conduction band of the absorbing region is in the range of about 1.4 eV to about 1.5 eV and an overall bandgap of the absorbing region is in the range of about 2.3 eV to about 2.4 eV. The substrate comprises n-type GaP, the hole extraction region comprises n-type GaAsxP1-x where 0.35 not less than x not less than 0.6, the absorbing region comprises n-type GaAsxNcP1-x-c where 0.005 not less than c not less than 0.2, and 0.37 not less than x not less than 0.77 and the electron extraction region comprises p-type GaP. The substrate comprises n-type GaP, the hole extraction region comprises n-type GaAsxP1-x where 0.4 not less than x not less than 0.54, the absorbing region comprises n-type GaAsxNcP1-x-c where 0.015 not less than c not less than 0.05 and 0.47 not less than x not less than 0.67 and the electron extraction region comprises p-type GaP.