GaN devices with ion implanted ohmic contacts and method of fabricating devices incorporating the same
A method for activating implanted dopants and repairing damage to dopant-implanted GaN to form n-type or p-type GaN. A GaN substrate is implanted with n- or p-type ions and is subjected to a high-temperature anneal to activate the implanted dopants and to produce planar n- or p-type doped areas within the GaN having an activated dopant concentration of about 10 18 -10 22 cm −3 . An initial annealing at a temperature at which the GaN is stable at a predetermined process temperature for a predetermined time can be conducted before the high-temperature anneal. A thermally stable cap can be applied to the GaN substrate to suppress nitrogen evolution from the GaN surface during the high-temperature annealing step. The high-temperature annealing can be conducted under N 2 pressure to increase the stability of the GaN. The annealing can be conducted using laser annealing or rapid thermal annealing (RTA).
1. A method for selectively forming at least one n-doped region in an epitaxial GaN material layer, the method including the steps of:
selectively applying a mask to a predetermined region of the GaN material layer;
implanting n-type dopant ions into at least one predetermined unmasked region of the GaN material layer to form an n-implanted GaN material layer;
removing the mask from the n-implanted GaN material layer;
subjecting the n-implanted GaN material layer to a first annealing at a predetermined temperature at which the GaN is stable for a predetermined time of a few seconds to several hours; and
subsequently subjecting the n-implanted GaN material layer to a second annealing at a predetermined temperature between 900 and 1600° C. for a predetermined time between a few seconds and a few hours and at a predetermined pressure between about 1 atm and about 100 bar to activate the implanted n-dopant ions and to produce at least one electrically activated n-doped region within the GaN;
wherein the electrically activated n-doped region is planar to an upper surface of the epitaxial GaN material layer and has a concentration of activated implanted n-type dopant ions of about 10 18 cm −3 to about 10 22 cm −3 .
2. The method according to claim 1 , wherein the first annealing is conducted at a temperature of about 850° C. for several hours at atmospheric pressure.
3. The method according to claim 1 , wherein the first annealing is conducted at a temperature between about 850° C. and about 1050° C. for a few minutes at atmospheric pressure.
4. The method according to claim 1 , further including applying a thermally protective cap to an upper surface of the n-implanted GaN before annealing, the cap being configured to suppress evolution of nitrogen from the GaN during annealing.
5. The method according to claim 1 , further including applying a nitrogen overpressure of up to about 100 bar during the second annealing to further stabilize the GaN.
6. The method according to claim 1 , wherein the second annealing is conducted by means of laser annealing or rapid thermal annealing (RTA).
7. The method according to claim 1 , wherein the n-dopant ions comprise Si or Ge.
8. The method according to claim 1 , wherein the GaN material layer comprises unintentionally doped GaN, semi-insulating GaN, carbon-doped GaN, or an AlGaN/GaN heterostructure.
9. The method according to claim 1 , wherein the GaN material layer is situated on a substrate comprising GaN, SiC, Si, sapphire, or an engineered composite.