Doping of Czochralski-grown bulk β-Ga2O3 single crystals with Cr, Ce and Al

Abstract We experimentally evaluated segregation of Cr, Ce and Al in bulk β-Ga 2 O 3 single crystals grown by the Czochralski method, as well as the impact of these dopants on optical properties. The segregation of Cr and Ce and their incorporation into the β-Ga 2 O 3 crystal structure strongly depends on O 2 concentration in the growth atmosphere which has a noticeable impact on decomposition of Ga 2 O 3 and Cr 2 O 3 , as well as on the charge state of Cr and Ce. Effective segregation coefficients for Cr are in the range of 3.1–1.5 at 7–24 vol% O 2 , while for Ce they are roughly below 0.01 at 1.5–34 vol% O 2 . The effective segregation coefficient for Al is 1.1 at 1.5–21 vol% O 2 . Both dopants Ce and Al have a thermodynamically stabilizing effect on β-Ga 2 O 3 crystal growth by supressing decomposition. While Ce has no impact on the optical transmittance in the ultraviolet and visible regions, in Cr doped crystals we observe three absorption bands due to Cr 3+ on octahedral Ga sites, one in the ultraviolet merging with the band edge absorption of β-Ga 2 O 3 and two in the visible spectrum, for which we estimate the absorption cross sections. Al doping also does not induce dopant related absorption bands but clearly shifts the absorption edge as one expects for a solid-solution crystal Ga 2(1−x) Al 2x O 3 still in the monoclinic phase. For the highest doping concentration (Ga 1.9 Al 0.1 O 3 ) we estimate an increase of the energy gap by 0.11 eV.