Hydrogen gas obtained by the electrolysis of water has long been proposed as a clean and sustainable alternative to fossil fuels. Noble metals such as Pt are capable of splitting water at low overpotentials, but the implementation of inexpensive solar-driven water-splitting systems and electrolyzers could benefit from the development of robust, efficient, and abundant alternatives to noble metal catalysts. Transition metal phosphides (MxPy) have recently been identified as a promising family of Earth abundant electrocatalysts for the hydrogen-evolution reaction (HER) and are capable of operating with low overpotentials at operationally relevant current densities while exhibiting stability under strongly acidic conditions. In this review, we highlight the progress that has been made in this field and provide insights into the synthesis, characterization, and electrochemical behavior of transition metal phosphides as HER electrocatalysts. We also discuss strategies for the incorporation of metal phosphides ...

Synthesis, Characterization, and Properties of Metal Phosphide Catalysts for the Hydrogen-Evolution Reaction

Optical, crystallographic, and transport properties of nominally undoped n‐type and Zn doped p‐type Gax In1−xAs /InP (0.44<x<0.49) grown by liquid phase epitaxy (LPE), vapor phase epitaxy (VPE), and metal organic chemical vapor deposition (MOCVD) have been studied and related to the different growth methods. Samples grown by LPE show in general much larger luminescence intensities than the VPE samples with similar impurity concentration and less structural and compositional inhomogeneities. Peaks related to free and bound excitons and to different impurities are found in the photoluminescence and absorption spectra of the undoped samples. The binding energy of the exciton is determined to be 2.1±0.1 meV, in agreement with hydrogenic theory. A longitudinal optical (LO) phonon energy of 32±0.5 meV is derived from LO‐phonon replica of the exciton line. The dependence of the energy gap at T=2 K from the solid solution composition in the range xGa =45%–49% is determined yielding a bowing parameter of C=0.475 a...

Optical and crystallographic properties and impurity incorporation of GaxIn1−xAs (0.44<x<0.49) grown by liquid phase epitaxy, vapor phase epitaxy, and metal organic chemical vapor deposition

The metalorganic chemical vapor deposition (MOCVD) of epitaxial III‐V semiconductor alloys on III‐V substrates is reviewed in detail. The emphasis is placed on both practical and theoretical knowledge of the equipment and deposition process. The chemistry of the source alkyls and the dynamics of the transport process are discussed. The growth of the GaAs and AlxGa1−xAs systems are treated as prototypical examples (and the most studied) of the III‐V materials. Latter sections review InP, Ga1−xInxAs, and related alloys. Finally, the antimonide and the other systems are reviewed. Electronic and optical devices fabricated from MOCVD‐grown materials are used as examples of the capabilities of the growth technique.

Metalorganic chemical vapor deposition of III‐V semiconductors

A new epitaxial growth technique, chemical beam epitaxy (CBE), was demsonstrated and investigated with the growth of InP and GaAs. In this technique, all the sources were gaseous group III and group V alkyls. The In and Ga were derived by the pyrolysis of either trimethylindium or triethylindium and trimethylgallium or triethylgallium at the heated substrate surface, respectively. The As2 and P2 were obtained by thermal decomposition of triethylphosphine and trimethylarsine in contact with heated Ta or Mo at 950–1200 °C, respectively. Unlike conventional vapor phase epitaxy, in which the chemicals reach the substrate surface by diffusing through a stagnant carrier gas boundary layer above the substrate, the chemicals in CBE were admitted into a high vacuum growth chamber and impinged directly light of sight onto the heated substrate surface in the form of molecular beams. The beam nature of CBE resulted in efficient use of the impinging chemicals and allowed the utilization of mechanical shutters. A gas h...

Chemical beam epitaxy of InP and GaAs

A critical appraisal of growth mechanisms in MOVPE

The low pressure metalorganic chemical vapor deposition epitaxial growth and characterization of InP, Ga0.47In0.53 As and GaxIn1-xAsyP1-y, lattice-matched to InP substrate are described. The layers were found to have the same etch pit density (EPD) as the substrate. The best mobility obtained for InP was 5300 cm2 V−1S−1 at 300 K and 58 900 cm2 V−1 S−1 at 772K, and for GaInAs was 11900 cm2 V−1 S−1 at 300 K, 54 600 cm2 V−1 S−1 at 77 K and 90 000 cm V−1S−1 at 2°K. We report the first successful growth of a GaInAs-InP superlattice and the enhanced mobility of a two dimensional electron gas at a GaInAs -InP heterojunction grown by LP-MO CVD. LP MO CVD material has been used for GaInAsPInP, DH lasers emitting at 1.3 um and 1.5 um. These devices exhibit a low threshold current, a slightly higher than liquid phase epitaxy devices and a high differential quantum efficiency of 60%. Fundamental transverse mode oscillation has been achieved up to a power outpout of 10 mW. Threshold currents as low as 200 mA dc have been measured for devices with a stripe width of 9 um and a cavity length of 300 um for emission at 1.5 um. Values of T in the range 64–80 C have been obtained. Preliminary life testing has been carried out at room temperature on a few laser diodes (λ = 1.5μm). Operation at constant current for severalthousand hours has been achieved with no change in the threshold current.

Low pressure metalorganic chemical vapor deposition of InP and related compounds

In this paper it is shown that the low pressure organometallic chemical vapor deposition (LP-MOCVD) technique of growing semiconductors is generally applicable to most of the III-V compounds that are currently of interest. The principles of the technique and five selected specific applications are detailed: 1) GaAlAs/GaAs quantum well lasers; 2) GaAlAs/GaAs modulation doped structures; 3) Two dimensional electron gas layer at GalnAs/InP interfaces; 4) Low threshold-current density lasers operating at 1.3µ,m; 5) Multiquantum well GalnAs/InP heterostructures.

J. P. Duchemin

Papers

Low pressure metalorganic chemical vapor deposition of InP and related compounds

Metal Organic Chemical Vapor Deposition