InP-based semiconductor materials belong to promising candidates for wider use in optoelectronic devices. Parameters of the devices are determined to a large degree by properties of component materials and by technology employed in the fabrication process. Contemporary science offers an extended array of procedures designed to achieve excellent quality of bulk and layer materials. We exploit specific properties of some rare earth elements (REE) in the preparation of InP layers by liquid phase epitaxy (LPE). Dealing with REE in III-V semiconductors, two approaches are usually used. The first approach takes advantage of the gettering properties of REE. The extraordinarily high chemical reactivity of REE can be used for the removal of unwanted impurities from semiconductor compounds. Combined with appropriate technology, additions of REE have been shown to lead to pure semiconductor materials of both conductivity types [1]. We proposed the application of InP-based structures in the fabrication of radiation detectors [2]. The second approach exploits specific luminescence properties of REE when incorporated into the lattice of the crystalline semiconductor material. REE doped semiconductors show sharp luminescence due to the intra-4f-shell transitions. Focusing on InP layers prepared by LPE, the incorporation of REE was confirmed in the case of Yb doping [3]. Photoluminescence (PL) and electrical measurements indicated successful incorporation on Ce doped layers [4]. In most cases, however, REE do not enter the InP lattice.

InP single crystal layers were grown by LPE on (100) oriented InP:Sn and InP:Fe substrates with Pr, Ce, and Yb addition to the melt. The growth process was commenced under flowing high-purity hydrogen at a temperature of 660 °C with a cooling rate of 0.7 °Cmin^-1. The metallic REE was mechanically embedded into the melt to prevent its contact with the surrounding ambient at the stage before the growth process to reduce the high affinity of REE especially towards oxygen and hydrogen.

We focused on the characterization of InP epitaxial layers by photoluminescence (PL) and secondary ion mass spectroscopy (SIMS) in order to explain: (i) the gettering effect and conductivity crossover for Pr treated samples, (ii) the incorporation of REE into the InP lattice for Yb and Ce treated samples. Information about chemical homogeneity of the layers was provided by the measurement of the depth concentration profile by SIMS. The concentration profile was determined for the applied REE and typical electrically active impurities. We analyzed and distinguished native and impurity-related defects from those introduced by REE admixture.

We conclude that a significant improvement of the InP layer purity with addition of Pr into the growth melt was observed. PL spectra were markedly narrowed and fine spectral features were resolved. The incorporation of Yb and Ce into the InP lattice was confirmed by PL and SIMS.

The work has been supported by the grant of the Academy of Sciences of the Czech Republic AV0Z 20670512-I054 and by the Czech Science Foundation grant 102/06/0153.

[1] Zakharenkov, L.; Kozlovskii, V.; Gorelenok, A.; Shmidt, N.: Rare-earth elements in the technology of III-V compounds 1997, 91-130
[2] Procházková, O.; Grym, J.; Zavadil, J.; Zdánský, K.: Journal of Crystal Growth, 2005, 275, e959
[3] Korber, W. et al.: Journal of Crystal Growth, 1986, 79, 741
[4] Zavadil, J.; Procházková, O.; Gladkov, P.: Crystal Research & Technology, 2005, 40, 498

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