Liquid phase epitaxy by conventional tipping technique has been employed for the growth of high purity InP epitaxial layers. The layers were grown at 720~176on (100) and (111) oriented InP substrates. Characteristic surface structures for the substrate orientations as a function of the growth temperature were observed. The layers were characterized by Hall data and photoluminescence measurements at low temperatures. The simultaneous observation of the band-acceptor and donor-acceptor pair transition due to the main acceptor in our LPE-layers is reported. The binding energy of this acceptor is determined to EA1 = 41.0 meV (• meV).During the last years there has been an increasing interest in high purity epitaxial layers of InP, for instance for Gunn effect applications (1). So far, high purity epitaxial layers were grown by vapor phase epitaxy in particular by the Effer method (2, 3). Net electron concentrations of n --4 9 1014 cm -~ and mobilities of ~77K : 87,000 cm 2 V -1 sec -1 were obtained. In the case of GaAs liquid phase epitaxy (LPE) has been very successful in the preparation of high purity epitaxial layers (4-8). One should therefore expect similar good results for the case of InP. In this paper the growth of high purity InP layers is described in connection with Hall data and photoluminescence measurements at low temperatures. Previous works on InP LPE were done by several authors (9-11). The best values for the LPE-layers with ND --NA ----2 9 1015 cm -3 and ~77K ----49,000 cm 2 V-' see-' were reached by Wood et al. (11). Recently Astles et al. (12) have reported on the growth of InP by LPE from solutions saturated with P from PH3. Values of ND --NA ----3 9 10 '5 cm -3 and #77 ----27,000 cm 2 V-' see -1 have been reported.
LPE--Apparatus and Experimental ProcedureThe experience from LPE growth of high purity GaAs has been that the growth results are strongly influenced by the way in which the growth process is performed (13,14). Important steps are: (i) heating of In-InP solution, (ii) preparation of the single-crystal substrate, (iii) equilibration and homogenization of the solution, and (iv) tipping the solution on the substrate. In the following we describe the corresponding conditions for InP-LPE. For the growth experiments we used a tipping system (14) (schematically shown in Fig. 1). The reaction tube was made of suprasil quartz, the boat for the In-InP solution of high purity graphite. The tube and boat were locked together and could be rotated around the long axis for immersion and withdrawal of the substrate from the solution. To avoid air leaks we used a Pyrex spiral which allowed the rotation of the tube without moving joints. The furnace was transparent (15) in order to observe substrate and solution. The graphite boat was heated at T ----1600~ under a vacuum of 10 -6 Torr for 3 hr. After that, the boat was loaded with 6N In (Johnson Matthey Limited, England) and baked at T : 730~ in the reaction tube for 10 hr under a Pd-diffused H2 gas flow. At the end of this procedure the boat was coole...