Group III nitride substrate with oxygen gradient, method of making, and method of use
Embodiments of the present disclosure include techniques related to techniques for processing materials for manufacture of group-III metal nitride and gallium based substrates. More specifically, embodiments of the disclosure include techniques for substrates with a controlled oxygen gradient using a combination of processing techniques. Merely by way of example, the disclosure can be applied to growing crystals of GaN, AlN, InN, InGaN, AlGaN, and AlInGaN, and others for manufacture of bulk or patterned substrates. Such bulk or patterned substrates can be used for a variety of applications including optoelectronic and electronic devices, lasers, light emitting diodes, solar cells, photo electrochemical water splitting and hydrogen generation, photodetectors, integrated circuits, and transistors, and others.
1. A free-standing crystal, comprising a group III metal and nitrogen, wherein the free-standing crystal comprises:
a wurtzite crystal structure;
a first surface having a maximum dimension greater than 40 millimeters in a first direction and a crystallographic orientation within 10 degrees of (0 0 0 1); and
a second surface on the opposite side of the crystal from the first surface, wherein a separation between the first surface and the second surface is between about 200 micrometers and about 2000 micrometers,
wherein an average oxygen concentration within a depth of 2 to 10 micrometers from the first surface, measured at at least four regions, is between 1×10 16 cm −3 and 5×10 19 cm −3 and is greater, by a factor between about 1.1 and about 10, than the average oxygen concentration within a depth of 2 to 10 micrometers from the second surface, measured at at least four regions, as quantified by calibrated secondary ion mass spectrometry.
2. The free-standing crystal of claim 1 , wherein the average oxygen concentration within a depth of 2 to 10 micrometers on the first surface is greater, by a factor between about 1.1 and about 3, than the average oxygen concentration within a depth of 2 to 10 micrometers on the second surface, as quantified by calibrated secondary ion mass spectrometry.
3. The free-standing crystal of claim 1 , wherein the crystal further comprises an impurity concentration of H greater than 10 17 cm −3 , and an impurity concentration of at least one of Li, Na, K, F, Cl, Br, and I greater than 10 15 cm −3 , as quantified by calibrated secondary ion mass spectrometry within a depth of 2 to 10 micrometers on the first surface, measured at at least four regions.
4. The free-standing crystal of claim 1 , wherein the first surface is characterized by an average impurity concentrations of:
hydrogen (H) between 1×10 16 cm −3 and 8×10 19 cm −3 ; and
at least one of fluorine (F) and chlorine (Cl) between 1×10 15 cm −3 and 1×10 19 cm −3 .
5. The free-standing crystal of claim 1 , wherein the first surface is characterized by impurity concentrations of:
hydrogen (H) between 1×10 16 cm −3 and 8×10 19 cm −3 ; and
at least one of sodium (Na) and potassium (K) between 3×10 15 cm −3 and 1×10 18 cm 3 .
6. The free-standing crystal of claim 3 , wherein a ratio of the impurity concentration of H to an impurity concentration of O is between about 0.3 and about 10.
7. The free-standing crystal of claim 6 , wherein a ratio of the impurity concentration of H to an impurity concentration of O is between about 0.4 and about 5.
8. The free-standing crystal of claim 4 , wherein a ratio of the impurity concentration of F to an impurity concentration of O is between about 0.05% and about 10%.
9. The free-standing crystal of claim 4 , wherein a ratio of the impurity concentration of F to an impurity concentration of O is between about 0.1% and about 6%.
10. The free-standing crystal of claim 4 , wherein a ratio of the impurity concentration of F to an impurity concentration of O is between about 0.2% and about 1%.
11. The free-standing crystal of claim 1 , wherein the average oxygen concentration on the second surface is above about 1×10 18 cm −3 .
12. The free-standing crystal of claim 1 , wherein an oxygen gradient, defined as a difference between the average oxygen concentration within a depth of 2 to 10 micrometers on the first surface and the average oxygen concentration within a depth of 2 to 10 micrometers on the second surface divided by a separation distance of between the first surface and the second surface, is between about 1×10 21 cm −4 and about 5×10 16 cm −4 .
13. The free-standing crystal of claim 12 , wherein the oxygen gradient is between about 5×10 20 cm −4 and about 2×10 17 cm −4 .
14. The free-standing crystal of claim 12 , wherein the oxygen gradient is between about 2×10 20 cm −4 and about 1×10 18 cm −4 .
15. The free-standing crystal of claim 1 , wherein the first surface and the second surface are substantially free of implantation damage or plasma damage to a depth of about 10 micrometers.
16. The free-standing crystal of claim 1 , wherein the first surface has a maximum dimension greater than 90 millimeters in the first direction.
17. The free-standing crystal of claim 1 , wherein the separation between the first surface and the second surface is between about 250 micrometers and about 1000 micrometers.
18. The free-standing crystal of claim 1 , wherein the separation between the first surface and the second surface is characterized by a total thickness variation below about 20 micrometers.
19. The free-standing crystal of claim 1 , wherein a variation in miscut angle across the first surface is less than about 0.1 degree in each of two orthogonal crystallographic directions.
20. The free-standing crystal of claim 1 , wherein a root-mean-square surface roughness of the first surface, as measured over an area of at least 10 μm×10 μm, is less than about 0.1 nanometer.