20Congreso Nacional 
Sociedad Mexicana de Ciencia de Superficies y Vacío A.C.

Optical and Structural Properties of Highly Te-doped
InGaAsSb Epitaxial Layers

C. Rivera-Morales1, M. Rojas-López2, P. Rodríguez-Fragoso3, M.A. Vidal4, J.L. Herrera-Pérez2, and J.G. Mendoza-Alvarez5
1 IFUAP. Apdo. Postal J-48. Puebla, Pue. 72570. México
2 CICATA-IPN. Unidad Puebla. Acatlan 63, Col. La Paz. Puebla, Pue. 72160. México
3 CICATA-IPN. Unidad Legaria. Legaria 694. Col. Irrigación. Mexico DF 11500. Mexico
4 IICO-UASLP. San Luis Potosí, SLP. México
5Instituto Politécnico Nacional Unidad Profesional “Adolfo López Mateos” México, D.F.

 The system InGaAsSb/GaSb is being intensively investigated because of its potential application for the development of emission and detection optoelectronic devices in the medium infrared spectrum, such as semiconductor lasers and photodetectors. The bandgap energy of this quaternary alloy can be changed in the range 1.6-2.3 microns depending on the layer stoichiometry.
 The development of devices is based on the capability of grow n- and p-type InGaAsSb epitaxial layers. Undoped InGaAsSb layers present a p-type conductivity, and in order to get n-type layers, Te impurification is commonly used in the growth of those layers.
 InGaAsSb layers were grown using the liquid phase epitaxy technique on GaSb substrates. To dope the layers we used pellets of Sb3Te2 in preparing the growth melts. Using different amounts of Sb3Te2 in the melts we obtained epitaxial layers with different Te concentrations in the range: 1.0 – 2.5 at. %.
 High resolution X-ray diffraction measured on the samples showed that the lattice mismatch between layer and substrate changed with the layer Te content indicating a change in the zincblende structure when the Te atoms enter substitutionally in the As sites. From the Raman spectra measured at room temperature on the different samples it can be observed that as the Te concentration increases there appears a decrease in the Raman peak related to the LO-InAs phonon, as well as with the peak associated to the TO-GaAs phonon. This behavior is also an evidence of the substitutional character of Te atoms in the As sites. The optical properties of this set of samples were also characterized measuring the photoreflectance (PR) spectra at different temperatures, and from the fitting of the PR spectra to the theoretical lineshapes we determine the bandgap energy for each sample and their temperature dependence. It was obtained that the bandgap energy has a slight increase of about 50 meV which we believe is due to a band filling effect that takes place when the Fermi level enters into the conduction band because of the high Te doping. These effects are discussed in this work.

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