We have studied the mechanism of Be incorporation in InP homoepitaxial films grown by metalorganic molecular beam epitaxy. The actual Be concentration in the films reaches 1-2ϫ10 19 cm Ϫ3 while the hole concentration saturates at a lower value ͑ ϳ2ϫ10 18 cm Ϫ3 in our case͒. The measured lattice mismatch between film and substrate depends both on growth temperature and Be flux. The resulting changes in morphology suggest that the excess Be forms microclusters in the films grown at higher

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... ures-due to the higher surface mobility, leading to the growth of oval defects. Be rejection to the surface is also observed. The surfaces of samples with no cap layer present a granulation which may be related to the formation of a new phase like Be 3 P 2 . © 1995 American Institute of Physics. Beryllium ͑Be͒ is a widely used p-type dopant in ultrahigh vacuum systems like molecular beam epitaxy ͑MBE͒ and metalorganic MBE or chemical beam epitaxy ͑MOMBE/ CBE͒ due to its large sticking coefficient at usual growth temperatures. 1 Even though extremely high Be doping ͑Ͼ10 20 cm Ϫ3 ͒ has been achieved for InGaAs by several authors, 2-4 high Be doping in InP has shown to be difficult both due to the lower solid solubility of Be in InP 5 and to surface degradation. 6,7 We show here a study on the growth mechanisms leading eventually to the observed surface degradation using x-ray diffraction ͑XRD͒, atomic force microscopy ͑AFM͒, Auger and secondary ion mass spectrometry ͑SIMS͒. The InP films were grown on a MOMBE/CBE system from Riber using TMI, PH 3 and solid Be as group III, V and dopant sources, respectively. PH 3 was decomposed at a cracker cell at 950°C to provide P 2 as P precursor. Both nominally ͑001͒ oriented and 2°off towards nearest ͗110͘ direction InP:Fe substrates were used. The growth temperature T g for InP ͑in the range 500-530°C͒ was monitored using an infrared pyrometer. The samples were In-mounted on Mo blocks and the surface oxide was desorbed by heating the samples to 530°C under P 2 overpressure before growth. Growth rates were ϳ0.9 m/h. Samples considered here were ϳ0.9 m thick. The Be dopant cell temperature ͑ T Be ͒ was varied in the range 700-850°C. Figure 1 shows the Hall carrier concentration ͑ N A ϪN D ͒ for the InP:Be samples grown at 530°C. We can observe that for the lower T Be , the slope of the curve follows that of the Be vapor pressure. 2,8 At the highest T Be , however, a saturation in the electrical activation of the dopant is reached. The maximum carrier concentration ͑ϳ2ϫ10 18 cm Ϫ3 in our case͒ does not change for the growth temperatures considered here. Similar saturation in the dopant electrical activation and the dependence of maximum carrier concentration on growth temperature have been reported for Be doping of both InP and InGaAs. 2,9 Figure 2 shows Nomarski pictures of InP surfaces of doped and undoped samples grown at T g ϭ530°C. The change in surface morphology is quite obvious even at such low magnification scale. A corrugation can be observed on the doped sample in between the large pits; the density of these large pits corresponds to the oval defect density observed in the undoped samples. The oval defects form due to extraneous factors-like surface contamination or nonsto-a͒ Electronic mail: monica@ifi.unicamp.br FIG. 1. 300 K Hall carrier concentration for InP:Be samples grown at 530°C as a function of T Be . The slope of the curve follows that of Be vapor pressure ͑Ref. 8͒ and is the same observed by R. A. Hamm et al. for Bedoped InGaAs ͑Ref. 2͒.