Residual impurities in high purity InP grown by chemical beam epitaxy

In the past few years, chemical beam epitaxy (CBE) has succeeded in producing high purity InP with residual carrier concentrations in the low 10¹⁴ cm^-3 range and liquid nitrogen temperature mobilities much higher than 10⁵ cm²/Vs. The authors present the results of a study where they have combined electrical, chemical, and optical measurements to identify the residual impurities in InP layers grown with different growth parameters. It is shown that S and Si are the two major residual donor impurities in InP layers grown by CBE and that they originate from the gas sources. Arsenic contamination of InP layers is a common problem in gas source systems, particularly when a single cracker cell is used for both As and P sources. However this contamination can be greatly reduced with a thorough baking prior to InP growth. The concentration of acceptors is negligible and too low to allow the identification of the residual acceptor impurities. Under optimized growth conditions, InP layers with residual carrier concentrations less than 10¹⁴ cm ^-3 can be routinely grown with 77 K mobilities larger than 2 × 10⁵ cm²/Vs