| abstract |
An epitaxially grown compound-semiconductor crystal comprising a substrate, a buffer layer formed directly or indirectly on the substrate, and an active layer formed on the buffer layer. The buffer layer comprises (A) a high-resistivity AlGaAs or AlGaInP layer doped with oxygen or/and a transition metal and, formed thereon, (B) a layer consisting of high-purity GaAs, InGaP, or AlGaAs. |