Net donor and acceptor concentrations in InGaAs layers grown by liquid phase epitaxy from melts containing 0.1-0.18 wt% are estimated by fitting theoretically calculated temperature-dependent mobility with experimental data. Donors are reduced more drastically compared to the acceptors due to the impurity gettering action of Er and the grown layers turn out to be heavily compensated. The 77 K mobility do not increase much inspite of a very low free carrier concentration in the layers.