Gallium nitride single crystal substrate and method for producing the same
There is provided a gallium nitride single crystal substrate, which is a gallium nitride single crystal substrate having a diameter of 50 mm or more, with a low-index crystal plane closest to a main surface being (0001), and in which Ge concentration in the substrate is 3×10 18 cm −3 or more; and among peaks appearing in a histogram of diameters of etch pits during etching applied to the main surface with an alkaline etching solution, a first peak having a smallest diameter is a single peak having no shoulder.
1 . A gallium nitride single crystal substrate,
which is a gallium nitride single crystal substrate having a diameter of 50 mm or more, with a low-index crystal plane closest to a main surface being (0001), and
in which Ge concentration in the substrate is 3×10 18 cm −3 or more; and
among peaks appearing in a histogram of diameters of etch pits during etching applied to the main surface with an alkaline etching solution, a first peak having a smallest diameter is a single peak having no shoulder.
2 . The gallium nitride single crystal substrate according to claim 1 , wherein when a frequency of the first peak is A, there are two peaks appearing in the histogram having a frequency of A/10 or more, including the first peak.
3 . The gallium nitride single crystal substrate of according to claim 1 , wherein in histograms in a plurality of different regions on the main surface, the first peak is a single peak without a shoulder in all of the plurality of histograms.
4 . The gallium nitride single crystal substrate according to claim 1 , wherein, when an etch pit diameter of the first peak is a, in the histogram, the total number of etch pits having a diameter exceeding 4 a is 1/1000 or less of the number of the etch pits constituting the first peak.
5 . The gallium nitride single crystal substrate according to claim 1 , wherein an average density of the etch pits is less than 1×10 6 cm −2 .
6 . The gallium nitride single crystal substrate according to claim 1 , wherein the histogram is measured from a region having an area of 1 mm 2 or more.
7 . A method for producing a gallium nitride single crystal substrate, the method including the steps of:
(a) preparing a base substrate composed of a gallium nitride single crystal having (0001) that is a low-index crystal plane closest to a main surface;
(b) epitaxially growing the gallium nitride single crystal having a Ge concentration of 3×10 18 cm −3 or more on the main surface of the base substrate; and
(c) obtaining a gallium nitride single crystal substrate having a diameter of 50 mm or more, from the gallium nitride single crystal epitaxially grown in the step (b),
wherein in the step (b), a gas containing HCl is intermittently introduced to periodically etch a growth interface, thereby uniformly doping the crystal with Ge.