1. A semiconductor photocathode comprising a first III-V compound semiconductor layer and a second III-V compound semiconductor layer doped with a p-type impurity and joined to each other to make a heterojunction;
wherein the second III-V compound semiconductor layer functions as a light absorbing layer;
wherein an energy gap of the second III-V compound semiconductor layer is smaller than an energy gap of the first III-V compound semiconductor layer; and
wherein beryllium (Be) or carbon (C) is used as the p-type dopant in the first III-V compound semiconductor layer and the second III-V compound semiconductor layer.
2. The semiconductor photocathode according to claim 1, wherein the second III-V compound semiconductor layer is deposited on the first III-V compound semiconductor layer.
3. The semiconductor photocathode according to claim 1, wherein the first III-V compound semiconductor layer and the second III-V compound semiconductor layer contain at least one from each group of (In, Ga, Al) and (As, P, N).
4. The semiconductor photocathode according to claim 1, wherein the first III-V compound semiconductor layer is a III-V compound semiconductor layer of a binary compound semiconductor, and
wherein the second III-V compound semiconductor layer is a III-V compound semiconductor layer of a ternary compound semiconductor or a quaternary compound semiconductor.
5. The semiconductor photocathode according to claim 1, wherein the first III-V compound semiconductor layer and the second III-V compound semiconductor layer are grown by molecular beam epitaxy.
6. The semiconductor photocathode according to claim 1, wherein the first III-V compound semiconductor layer and the second III-V compound semiconductor layer are doped with the p-type impurity in a low concentration of not more than 1\xd71018 cm\u22123.
7. The semiconductor photocathode according to claim 1, comprising:
a transparent substrate:
an entrance electrode formed above the transparent substrate and permitting passage of light having passed through the transparent substrate;
said light absorbing layer of the second III-V compound semiconductor layer formed above the entrance electrode and adapted for exciting photoelectrons in response to incidence of light;
a window layer of a p-type III-V compound semiconductor material interposed between the entrance electrode and the light absorbing layer, having an energy gap larger than that of the light absorbing layer, comprised of a semiconductor material to be lattice-matched with the light absorbing layer, and having a thickness of not less than 10 nm nor more than 200 nm;
an electron transport layer of the first III-V compound semiconductor layer formed on the light absorbing layer, comprised of a semiconductor material to be lattice-matched with the light absorbing material, and adapted for emitting the photoelectrons excited in the light absorbing layer, from a surface thereof to the outside; and
an emission electrode formed above the electron transport layer.
8. The semiconductor photocathode according to claim 1, comprising:
a transparent substrate:
an entrance electrode formed above the transparent substrate and permitting passage of light having passed through the transparent substrate;
said light absorbing layer of the second III-V compound semiconductor layer formed above the entrance electrode and adapted for exciting photoelectrons in response to incidence of light;
a window layer of a p-type III-V compound semiconductor material interposed between the entrance electrode and the light absorbing layer, having an energy gap larger than that of the light absorbing layer, comprised of a semiconductor material to be lattice-matched with the light absorbing layer, and having a thickness of not less than 10 nm nor more than 200 nm;
an electron transport layer of the first III-V compound semiconductor layer formed on the light absorbing layer, comprised of a semiconductor material to be lattice-matched with the light absorbing material, and adapted for emitting the photoelectrons excited in the light absorbing layer, from a surface thereof to the outside;
an emission electrode formed above the electron transport layer; and
a contact layer of an n-type III-V compound semiconductor material formed between the electron transport layer and the emission electrode.
9. The semiconductor photocathode according to claim 7, wherein the entrance electrode is a metal material having a thickness of not less than 5 nm nor more than 100 nm.
10. The semiconductor photocathode according to claim 7, wherein the entrance electrode is a metal material having a thickness of not less than 10 nm nor more than 50 nm.
11. The semiconductor photocathode according to claim 7, wherein the entrance electrode is a metal material layer having an aperture.
12. The semiconductor photocathode according to claim 7, wherein the entrance electrode is a layer of at least one transparent electroconductive material selected from a group consisting of ITO, ZnO, In2O3, and SnO2.
13. The semiconductor photocathode according to claim 7, wherein the thickness of the window layer is not less than 20 nm nor more than 100 nm.
14. The semiconductor photocathode according to claim 7, further comprising an insulating film or an antireflection film interposed between the transparent substrate and the entrance electrode.
15. The semiconductor photocathode according to claim 8, wherein the entrance electrode is a metal material having a thickness of not less than 5 nm nor more than 100 nm.
16. The semiconductor photocathode according to claim 8, wherein the entrance electrode is a metal material having a thickness of not less than 10 nm nor more than 50 nm.
17. The semiconductor photocathode according to claim 8, wherein the entrance electrode is a metal material layer having an aperture.
18. The semiconductor photocathode according to claim 8, wherein the entrance electrode is a layer of at least one transparent electroconductive material selected from a group consisting of ITO, ZnO, In2O3, and SnO2.
19. The semiconductor photocathode according to claim 8, wherein the thickness of the window layer is not less than 20 nm nor more than 100 nm.
20. The semiconductor photocathode according to claim 8, further comprising an insulating film or an antireflection film interposed between the transparent substrate and the entrance electrode.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A method of micromachining an electrolyte sheet comprising:
sintering the electrolyte sheet;
supporting the sintered electrolyte sheet; and
micromachining the sintered electrolyte sheet with a laser having a wavelength of less than 400 nm, a fluence of between 5 Joulescm2 and 200 Joulescm2, a repetition rate of between 30 Hz and 200 kHz and a pulse duration of between 1 ns and 100 ns.
2. The method of micromachining an electrolyte sheet according to claim 1, wherein said laser is a 355 nm nanosecond laser.
3. The method of micromachining an electrolyte sheet according to claim 2, wherein said laser has a repetition rate of at least 1 KHz, and cutting speed >50 mmsec.
4. A method of making multiple fuel cell devices, wherein multiple fuel cell devices (i) are at least partially fabricated on a single sheet of electrolyte; and (ii) are laser cut, separating them from one another according to the micromachining method of claim 1.
5. The method of micromachining an electrolyte sheet according to claim 1, said method including cutting off by micromachining more than 1 mm of at least one side of the electrolyte sheet, so as to remove at least a portion of electrolyte sheet edge curl.
6. The method of micromachining an electrolyte sheet according to claim 1, wherein the micromachining is performed by ablation in conjunction with auto-cleaving.
7. The method of micromachining an electrolyte sheet according to claim 1, wherein said micromachining includes cutting holes or trimming perimeter of the electrolyte sheet trough its entire thickness.
8. The method of micromachining an electrolyte sheet according to claim 1, wherein said electrolyte sheet is a corrugated sheet and said micromachining method produces via holes in said electrolyte sheet.
9. The method of micromachining an electrolyte sheet according to claim 1, including a step of laser micromachining at least one additional layer situated on said electrolyte sheet.
10. The method of micromachining an electrolyte sheet according to claim 7, wherein said holes are produced with a lip and said lip is trimmed off with a laser to a height of less than 5 \u03bcm.
11. The method of micromachining an electrolyte sheet according to claim 1, wherein the electrolyte sheet comprises a body of no more than 45 \u03bcm thick.
12. The method of micromachining an electrolyte sheet according to claim 1, wherein the electrolyte sheet is zirconia based.
13. The method of micromachining an electrolyte sheet according to claim 1, wherein the wavelength of the laser is between 200 nm and 300 nm.
14. The method of micromachining an electrolyte sheet according to claim 1, wherein the repetition rate of the laser is between 30 kHz and 200 kHz.
15. The method of micromachining an electrolyte sheet according to claim 1, wherein the fluence of the laser is less than 26 Joulescm2.
16. The method of micromachining an electrolyte sheet according to claim 1, wherein micromachining the sintered electrolyte sheet with a laser includes scanning a laser beam across a surface of the electrolyte sheet.
17. The method of claim 1, wherein the sintered electrolyte sheet is micromachined by drilling via holes through a thickness of the sintered electrolyte sheet with the laser using a multi-pass laser drilling technique at a wavelength of less than 400 nm, a fluence of between 5 Joulescm2 and 200 Joulescm2, a repetition rate of between 30 Hz and 200 kHz, and a pulse duration of between 1 ns and 100 ns.
18. The method of claim 17, wherein the sintered electrolyte sheet is micromachined by drilling via holes through a thickness of the sintered electrolyte sheet with the laser using a multi-pass laser drilling technique at a wavelength of less than 400 nm, a fluence of between 5 Joulescm2 and 200 Joulescm2, a repetition rate of between 30 Hz and 200 kHz, a pulse duration of between 1 ns and 100 ns, a laser speed >30 mmsec, and a pulse energy <60 \u03bcJ.
19. The method of claim 17, wherein the multi-pass laser drilling technique is a trepanning drilling technique.
20. The method of claim 17, wherein the multi-pass laser drilling technique is a helical drilling technique.
21. The method of claim 1, wherein the sintered electrolyte sheet is micromachined by scoring and fracturing the sintered electrolyte sheet with the laser at a wavelength of less than 400 nm, a fluence of between 5 Joulescm2 and 200 Joulescm2, a repetition rate of between 30 Hz and 200 kHz, and a pulse duration of between 1 ns and 100 ns, to form an edge surface that exhibits a combination of fracture and ablation, with more than 50% fracture and less than 50% ablation.
22. The method of claim 21, wherein the sintered electrolyte sheet is micromachined by scoring and fracturing the sintered electrolyte sheet with the laser at a cutting speed >30 mmsec.
23. The method claim 1, wherein the sintered electrolyte sheet is micromachined by ablating the electrolyte sheet at a wavelength of less than 400 nm, a fluence of between 5 Joulescm2 and 200 Joulescm2, a repetition rate of between 30 Hz and 200 kHz, and a pulse duration of between 1 ns and 100 ns to form an ablated edge surface having a grain size of less than about 2 \u03bcm.