Limits of doping In$_{0.53}$Ga$_{0.47}$As with Si and Be

We report on a study of doping efficiency in In$_{0.53}$Ga$_{0.47}$As layers grown on InP (001) substrates by molecular beam epitaxy. Si and Be effusion cells were used to provide n- and p-type dopants, respectively. In epilayers grown at 0.63 monolayers per second with a substrate temperature of 500\r{ }C, doping cell temperatures below T$_{Si}$=1260\r{ }C (T$_{Be}$=907\r{ }C) resulted in electron (hole) concentrations that followed an Arrhenius relation with an activation energy of 5.0 eV (4.0 eV). At higher cell temperatures, the carrier concentration saturated at approximately n=3.1$\times $10$^{19}$cm$^{{\-}3}$ (p=2.6$\times $10$^{19}$cm$^{{\-}3})$. For T$_{Si}$=1300\r{ }C (T$_{Be}$=928\r{ }C), the carrier concentration was increased to n=4.2$\times $10$^{19}$cm$^{{\-}3}$ (p=3.3$\times $10$^{19}$cm$^{{\-}3})$ through use of a lower substrate temperature of 400\r{ }C (470\r{ }C). The maximum carrier concentration achieved through lowering the substrate temperature was n=4.8$\times $10$^{19}$cm$^{{\-}3}$ (p=9.1$\times $10$^{19}$cm$^{{\-}3})$. For Be doping, the maximum hole concentration was increased to 1.3$\times $10$^{20}$cm$^{{\-}3}$ by using a lower growth rate. We will compare our results with the doping of GaSb and InAs, and discuss attempts to increase the maximum concentration through delta-doping and migration enhanced epitaxy.