Ultra long lifetime gallium arsenide
View Patent ↗A system and method for producing bulk GaAs with an increased carrier lifetime of at least 10 microseconds is provided. The system and method of producing the GaAs crystal involves using a technique called low pressure hydride vapor phase epitaxy (LP-HVPE). In this technique, a gas containing Ga (typically GaCl) is reacted with a gas containing As (typically AsH 3 ) at the surface of a GaAs substrate. When grown under the proper conditions, the epitaxial, vapor grown GaAs crystal has ultra-long free carrier lifetimes of at least one order of magnitude greater than that of the previous lifetime of 1 microsecond. This very long free carrier lifetime GaAs will be particularly useful as a semiconductor radiation detector material and is also expected to be useful for many other applications than include medical imaging, solar cells, diode lasers, and optical limiters and other applications.
1. A method of forming bulk gallium arsenide (GaAs) having a carrier lifetime of at least 10 microseconds comprising:
providing a low-pressure hydride vapor epitaxy (HVPE) system including a reaction chamber;
providing an arsine source;
providing a gallium chloride source;
delivering arsine (AsH3) from the arsine source to a substrate inside the reaction chamber;
delivering gallium chloride (GaCl) from the gallium chloride source to the substrate;
delivering AsH3 orthogonally relative to the GaCl directly at the substrate surface; and
mixing and effecting a reaction of the gallium chloride with the arsine directly at the substrate surface to create bulk GaAs having a carrier lifetime of at least 10 microseconds.
2. The method of claim 1 , wherein mixing and effecting the reaction of the gallium chloride with the arsine directly at the substrate surface is accomplished by a close-coupled shower-head apparatus delivering the gallium chloride to mix with arsine flowing across the wafer surface.
3. The method of claim 1 , further comprising:
growing bulk GaAs to a thickness greater than 500 micrometers.
4. The method of claim 1 , wherein the substrate is an off-cut semiconductor substrate wafer, wherein an off-cut angle, relative to a primary crystallographic axis is greater than 1° .
5. The method of claim 4 , wherein the off-cut angle is in a range from 1° to 10° .
6. The method of claim 5 , wherein the off-cut angle is about 4° .
7. The method of claim 1 , further comprising:
precluding growth of parasitic Gallium Arsenide (GaAs) deposits on chamber walls of the low pressure HVPE system through direct delivery of gallium chloride via a close-coupled shower-head apparatus to react with arsine flowing across the wafer surface.
8. The method of claim 1 , further comprising:
minimizing the incorporation of Silicon (Si) and Oxygen (O) impurities to effectuate the long carrier lifetimes.
9. The method of claim 8 , further comprising:
precluding flow of hydrogen chloride (HCl) along silicon dioxide (SiO 2 ) chamber walls of the low pressure HVPE system.
10. The method of claim 8 , further comprising:
replacing silicon dioxide (SiO 2 ) with Pyrolytic Boron Nitride (PBN) in a main reaction zone of the reaction chamber of the low pressure HVPE system.
11. The method of claim 10 , wherein a shower-head apparatus delivering the gallium chloride to react with arsine at the substrate surface is fabricated from PBN.
12. The method of claim 10 , wherein a susceptor is covered by PBN.
13. The method of claim 10 , further comprising:
rotating a satellite disc that supports a wafer holder and wafer from below, wherein the wafer holder is fabricated from PBN.
14. The method of claim 1 , further comprising providing a recessed horizontal wafer holder.
15. The method of claim 14 , wherein the recessed horizontal wafer holder reduces back-side impurity vapor transport from the substrate.
16. The method of claim 1 , further comprising:
rotating the substrate, wherein the substrate is rotated during GaAs growth.
17. The method of claim 16 , wherein the wafer is rotated to enhance mixing of the reacting GaCI and AsH 3 gases.
18. The method of claim 16 , wherein the wafer is rotated to achieve bulk GaAs with uniform composition and thickness.
19. The method of claim 16 , wherein the wafer is rotated by flowing inert gas over grooves on the underside of the satellite disc that supports the wafer.