A gallium arsenide single crystal substrate having a main surface, in which a ratio of the number of As atoms existing as diarsenic trioxide to the number of As atoms existing as diarsenic pentoxide is greater than or equal to 2 when the main surface is measured by X-ray photoelectron spectroscopy, in which an X-ray having energy of 150 eV is used and a take-off angle of a photoelectron is set to 5°. Arithmetic average roughness (Ra) of the main surface is less than or equal to 0.3 nm.

A gallium arsenide single crystal substrate having a main surface, in which a ratio of the number of As atoms existing as diarsenic trioxide to the number of As atoms existing as diarsenic pentoxide is greater than or equal to 2 when the main surface is measured by X-ray photoelectron spectroscopy, in which an X-ray having energy of 150 eV is used and a take-off angle of a photoelectron is set to 5°. Arithmetic average roughness (Ra) of the main surface is less than or equal to 0.3 nm.

A method comprising: forming a first mask over a substrate; forming one or more shadow walls in the openings of the first mask by selective area growth; forming a second mask over the substrate and shadow walls; forming a second material in the openings of the second mask by selective area growth; and depositing a layer of deposition material by angled deposition over parts of the substrate, shadow walls and second material, whereby regions shadowed by the shadow walls are left uncoated. In embodiments the second material may be a semiconductor and the deposition material may be a superconductor, and the method may be used to form one or more semiconductor-superconductor nanowires for inducing majorana zero modes as part of a quantum computing device.

A method comprising: forming a first mask over a substrate; forming one or more shadow walls in the openings of the first mask by selective area growth; forming a second mask over the substrate and shadow walls; forming a second material in the openings of the second mask by selective area growth; and depositing a layer of deposition material by angled deposition over parts of the substrate, shadow walls and second material, whereby regions shadowed by the shadow walls are left uncoated. In embodiments the second material may be a semiconductor and the deposition material may be a superconductor, and the method may be used to form one or more semiconductor-superconductor nanowires for inducing majorana zero modes as part of a quantum computing device.

A gas phase nanowire growth apparatus including a reaction chamber, a first input and a second input. The first input is located concentrically within the second input and the first and second input are configured such that a second fluid delivered from the second input provides a sheath between a first fluid delivered from the first input and a wall of the reaction chamber.

A gas phase nanowire growth apparatus including a reaction chamber, a first input and a second input. The first input is located concentrically within the second input and the first and second input are configured such that a second fluid delivered from the second input provides a sheath between a first fluid delivered from the first input and a wall of the reaction chamber.

A process for producing a monocrystalline layer of GaAs material comprises the transfer of a monocrystalline seed layer of SrTiO.sub.3 material to a carrier substrate of silicon material followed by epitaxial growth of a monocrystalline layer of GaAs material.

A process for producing a monocrystalline layer of GaAs material comprises the transfer of a monocrystalline seed layer of SrTiO.sub.3 material to a carrier substrate of silicon material followed by epitaxial growth of a monocrystalline layer of GaAs material.

A method of performing heteroepitaxy comprises exposing a substrate to a carrier gas, a first precursor gas, a Group II/III element, and a second precursor gas, to form a heteroepitaxial growth of one of GaAs, AlAs, InAs, GaP, InP, ZnSe, GaSe, CdSe, InSe, ZnTe, CdTe, GaTe, HgTe, GaSb, InSb, AlSb, CdS, GaN, and AlN on the substrate; wherein the substrate comprises one of GaAs, AlAs, InAs, GaP, InP, ZnSe, GaSe, CdSe, InSe, ZnTe, CdTe, GaTe, HgTe, GaSb, InSb, AlSb, CdS, GaN, and AlN; wherein the carrier gas is Hz, wherein the first precursor is HCl, the Group II/III element comprises at least one of Zn, Cd, Hg, Al, Ga, and In; and wherein the second precursor is one of AsH.sub.3 (arsine), PH.sub.3 (phosphine), H.sub.2Se (hydrogen selenide), H.sub.2Te (hydrogen telluride), SbH.sub.3 (hydrogen antimonide), H.sub.2S (hydrogen sulfide), and NH.sub.3 (ammonia). The process may be an HVPE (hydride vapor phase epitaxy) process.

A method of performing heteroepitaxy comprises exposing a substrate to a carrier gas, a first precursor gas, a Group II/III element, and a second precursor gas, to form a heteroepitaxial growth of one of GaAs, AlAs, InAs, GaP, InP, ZnSe, GaSe, CdSe, InSe, ZnTe, CdTe, GaTe, HgTe, GaSb, InSb, AlSb, CdS, GaN, and AlN on the substrate; wherein the substrate comprises one of GaAs, AlAs, InAs, GaP, InP, ZnSe, GaSe, CdSe, InSe, ZnTe, CdTe, GaTe, HgTe, GaSb, InSb, AlSb, CdS, GaN, and AlN; wherein the carrier gas is Hz, wherein the first precursor is HCl, the Group II/III element comprises at least one of Zn, Cd, Hg, Al, Ga, and In; and wherein the second precursor is one of AsH.sub.3 (arsine), PH.sub.3 (phosphine), H.sub.2Se (hydrogen selenide), H.sub.2Te (hydrogen telluride), SbH.sub.3 (hydrogen antimonide), H.sub.2S (hydrogen sulfide), and NH.sub.3 (ammonia). The process may be an HVPE (hydride vapor phase epitaxy) process.