Optical properties of vapor-grown Inx Ga1−xAs epitaxial films on GaAs and Inx Ga1−xP substrates

The absorption coefficients for In_x Ga_1−xAs epitaxial n ‐ and p‐type films have been determined for the composition range 0 < x < 0.25. The optical absorption coefficient is a parameter in the operation of negative electron affinity (NEA) photoemissive devices, and the experimentally determined absorption coefficient will be useful in the interpretation of NEA photoemissive device characteristics. In general, the optical absorption properties of n ‐ and p‐type In_x Ga_1−xAs alloys vary smoothly with increasing indium content. The effect of lattice parameter mismatch between the In_x Ga_1−xAs epitaxial film and GaAs or In_x Ga_1−xP substrates on the optical absorption properties is shown to be negligible. Doping with zinc acceptor impurities ${\text{([inverted lazy s]10}}^{19}\hspace{0.17em}{\mathrm{cm}}^{\text{−3}})$ does, however, apparently change slightly the characteristics of the In_x Ga_1−xAs absorption curves, particularly at low In compositions. Two nondestructive methods of determining the acceptor density of zinc‐doped GaAs epitaxial layers have been compared. The plasma minimum method is useful for acceptor concentrations above about 5 × 10¹⁸ cm⁻³, while the free‐carrier absorption method gives quantitative values in the 10¹⁷–10¹⁹‐cm⁻³ range.