Good quality In0.12Ga0.88As0.34P0.66 layers lattice matched to GaAs0.61P0.39 epitaxial substrates were grown by liquid-phase epitaxy. The electrical and optical properties of the un-, Te-, and Zn-doped In0.12Ga0.88As0.34P0.66 layers are described in detail. By selection of the optimum growth condition, we can obtain the undoped layer with an electron concentration of 2 x 10(16) cm-3. Room-temperature carrier concentrations ranging from 1.8 X 10(17) to 3.4 X 10(18) cm-2 for n-type and from 1.6 x 10(17) to 2.8 x 10(18) cm-3 for p-type dopants are obtained. The relative intensity of 300 K photoluminescence (PL) spectra presents the maximum values at 6 x 10(17) and 1 x 10(18) cm-3 for electron and hole concentrations, respectively The acceptor ionization energy for Zn also is described from the 50 K PL spectra. The five major emission peaks observed from the temperature dependence of PL spectra for the Zn-doped InGaAsP layer are identified clearly Finally, the p-n homostructure orange LEDs were fabricated to exhibit the emission peak wavelength and the full width at half maximum of electroluminescence of ca. 619 nm and 53 meV, respectively.