P. E. Gregory

High‐efficiency organometallic vapor phase epitaxy AlGaAs/GaAs monolithic cascade solar cell using metal interconnects

A two‐junction solar cell has been fabricated using an Al0.30Ga0.70As (1.82 eV) tap cell and a GaAs (1.43 eV) bottom cell. A processed metal interconnect is used to connect the two cells together in series. An efficiency of 21.5% at 980 mW/cm2 has been measured in a solar simulator with an open circuit voltage of 2.35 V, a short circuit current of 118.6 mA/cm2, and a fill factor of 0.76. An efficiency of 22% has been measured under 130 AM3 sun in a solar tracking concentrator. Organometallic vapor phase epitaxy is used to grow the entire nine‐layer device.

Field‐assisted photoemission to 2.1 microns from a Ag/p‐In0.77Ga0.23As photocathode

Reflection‐mode photoemission to a 2.1‐μm threshold has been achieved from an externally biased Ag/p‐In0.77Ga0.23As cathode. Quantum yield at 1.9 μm is 2×10−3 electrons per incident photon for 2.4‐V bias and a cathode cooled to ∼125 K. The cathode was grown by vapor‐phase epitaxy on a compositionally graded InAsP on InP (100) substrate using the hydride process.

Liquid‐phase‐epitaxial growth of lattice‐matched In0.53Ga0.47As on (100) ‐oriented InP

Growth of InGaAs lattice matched to InP was achieved for the first time on the (100) orientation of InP by liquid‐phase epitaxy. Growth conditions and melt composition for such a growth are presented. In0.53Ga0.47As/InP and InP/In0.53Ga0.47As/InP heterojunction structures for 1.7‐μm field‐assisted photocathodes have also been fabricated on (100) InP substrates.

High‐efficiency AlGaAs/GaAs concentrator solar cells by organometallic vapor phase epitaxy

Conversion efficiency of 23% at 369 suns has been achieved for packaged AlGaAs/GaAs solar cells fabricated by organometallic vapor phase epitaxy. The design considerations and the solar cell performance in concentrated sunlight are described.

Transferred‐electron photoemission to 1.65 μm from InGaAs

Photoemission to 1.65 μm has been achieved in the reflection mode from a bias‐assisted p‐InGaAs cathode. Quantum yield at 1.55 μm is ∼10−3 at 125 K and ∼10−4 at 300 K.

Quantum efficiency of InP field‐assisted photocathodes

Reflection‐mode quantum efficiencies have been calculated for the p‐InP bias‐assisted photoemitter (TE cathode) and have been found to be consistent with experimental data. The calculations, using Monte Carlo techniques, consider the transport of photogenerated electrons to the surface as well as the transmission of electrons at the surface into vacuum. Dependence of the predicted yield upon bias voltage and doping is discussed. Acceptor doping in the mid 1016/cm3 range is indicated as a good choice for a high quantum efficiency photocathode.

Field-assisted semiconductor photoemitters for the 1—2-µm range

Photoemission data and model calculations are presented for a field-assisted semiconductor photoemitter which has achieved reflection-mode quantum efficiencies as high as 8.0 percent at 1.55 µm. The cathodes are p-p heterostructures employing lattice-matched InP-InGaAsP alloys. A thin electron semitransparent Schottky barrier provides the biasing contact for field-assisted electron emission. Parameters for optimal photoemission and sources of dark-current emission are discussed.

The incorporation of Ga during LPE growth of In0.53Ga0.47As on (111)B and (100) InP substrates

We report the temperature dependence of the incorporation of Ga during LPE growth of In0.53Ga0.47As on (111) B‐ and (100) ‐oriented InP substrates. The distribution coefficients of Ga can be accurately represented by KGa(111)B =6.40×10−6 exp(1.10/kT) and KGa(100)=5.02×10−13 exp(2.37/kT), which are equal at 629 °C. The difference in activation energies is the source of the ’’discrepancy’’ reported by Pearsall etal. that KGa(111)B<KGa(100) at 621 °C while from our results KGa(111)B≳KGa(100) at 650 °C.

Ga0.80In0.20As 1.20‐eV high quantum efficiency junction for multijunction solar cells

A Ga0.80In0.20As junction for solar cell applications grown on GaAs by organometallic vapor phase epitaxy (OMVPE) with a peak collection quantum efficiency of 92% is reported. This junction is fabricated using step‐graded layers to reduce misfit dislocations between the junction and the substrate. The effects of step grading on the projected short circuit current density, peak quantum efficiency, and diode ideality factor have been measured. With grading, the ideality factor is reduced from n=2.7 to 1.2 for current densities greater than 0.01 A/cm2. This high‐performance Ga0.80In0.20As can serve as an excellent low‐gap junction for multijunction solar cells.

Transferred electron photoemission to 1.65 μ from an InGaAsP heterojunction cathode

Photoemission to 1.65 μ from a field‐assisted heterojunction cathode has been achieved for the first time. The all‐LPE‐grown cathode consists of a p‐type InGaAs photon‐absorbing electron‐generating layer, lattice matched to a p‐type InGaAsP transferred‐electron photoelectron‐emitting layer. Reflection‐mode quantum yield of ∼0.1% at 1.55 μ has been measured at 125 K.