Group III nitride stack
There is provided a Group III nitride stack in which the concentration of an impurity in the buffer/channel layer of an HEMT is suppressed to a predetermined range. The Group III nitride stack includes a first layer comprising gallium nitride, and a second layer on the first layer, the second layer comprising a Group III nitride having a lower electron affinity than gallium nitride. The first layer includes a lower layer and an upper layer on the lower layer. The carbon concentration in the upper layer is lower than a carbon concentration in the lower layer, the hydrogen concentration in the upper layer is lower than a hydrogen concentration in the lower layer, the carbon concentration in the upper layer is 5×10 16 cm −3 or less, and the hydrogen concentration in the upper layer is 1×10 17 cm −3 or less.
1. A Group III nitride stack comprising:
a first layer comprising gallium nitride; and
a second layer on the first layer, the second layer comprising a Group III nitride having a lower electron affinity than gallium nitride,
wherein the first layer includes a lower layer and an upper layer on the lower layer,
a carbon concentration in the upper layer is lower than a carbon concentration in the lower layer,
a hydrogen concentration in the upper layer is lower than a hydrogen concentration in the lower layer,
the carbon concentration in the upper layer is 5×10 16 cm −3 or less, and
the hydrogen concentration in the upper layer is 1×10 17 cm −3 or less.
2. The Group III nitride stack according to claim 1 ,
wherein the carbon concentration in the lower layer is higher than the carbon concentration in the upper layer by 2×10 16 cm −3 or more.
3. The Group III nitride stack according to claim 1 ,
wherein the carbon concentration in the lower layer is 5×10 17 cm −3 or less.
4. The Group III nitride stack according to claim 1 ,
wherein a ratio of the hydrogen concentration in the lower layer to the hydrogen concentration in the upper layer is 5:1 or less.
5. The Group III nitride stack according to claim 1 ,
wherein the hydrogen concentration in the lower layer is 1×10 18 cm −3 or less.
6. The Group III nitride stack according to claim 1 ,
wherein the carbon concentration in the upper layer is lower than the hydrogen concentration in the upper layer.
7. The Group III nitride stack according to claim 1 ,
wherein the carbon concentration in the lower layer is lower than the hydrogen concentration in the lower layer.
8. The Group III nitride stack according to claim 1 ,
wherein a silicon concentration in the upper layer is higher than a silicon concentration in the lower layer.
9. The Group III nitride stack according to claim 1 ,
wherein a silicon concentration in the upper layer is 5×10 14 cm −3 or more.
10. The Group III nitride stack according to claim 1 ,
wherein a silicon concentration in the lower layer is less than 5×10 14 cm −3 .