Growth by the CSVT (close-spaced vapor transport) technique and characterization of epitaxial GaAs layers on Ge substrates

Abstract

Epitaxial layers of GaAs on (100) GaAs substrates can be grown by close-spaced vapor transport using water vapor as the transporting agent. The parameters for the transport are Ti = 755°C. AT' = 45°C. and 6 = 0.03 cm (where Ti is the temperature of the graphite heating the substrate; AT', the temperature difference between the graphite heating the source and the one heating the substrate; and 6. the thickness of the spacer separating the GaAs source and the substrate). Mirrorlike epitaxial layers of GaAs are obtained with these parameters when water vapor, at a partial pressure of 4.58 Torr ( 1 Torr = 133.3 Pa), is introduced with H, at the beginning of the temperature rise of the reactor. The dimensions of the epitaxial layer are only limited by the size of the reactor. Using the same growth conditions. it is not possible to obtain mirrorlike films of GaAs on (100) Ge substrates. Instead, the layers are dull grey (sample no. I ) . It is howcder not a polycrystalline deposition since the pole figures, obtained by X-ray diffraction. reveal only four crystallographic orientations: {loo} the main one. {221} the secondary one, and {021} + {I 12) two minor contributions. Mirrorlike films of GaAs on (100) Ge substrates of less than 1 cni' have been obtained with T: = 775OC. AT' = 25°C. and 6 = 0.03 cm. With these conditions, the growth rate is 0.25 + 0.08 k m m i n I . The time evolution of T: and AT', froni room temperature up to the equilibrium temperature also influences the surface morphology of GaAs films on Ge while this was not the case for GaAs films on GaAs substrates. When the Ge substrate is larger than I cm'. the centre of the film becomes textured but the edges reniain mirrorlike (sample no. 2). Pole figures obtained for the center and the edges of sample no. 2 are similar. They are characterized by one large diffraction due to the (100) orientation. A few random crystallographic orientations and sometimes the {221} orientation, however, bearly emerge froni the background of these pole figures. Also transmission electron microscopy does not reveal any major difference between the center and the edges of sample no. 2. The density of threading dislocations is the sanie for both regions, varying from 10' c m ', close (2-3 k m ) to the interface, to lo7 c m ' in the thickness of the film. No misfit dislocations were observed.Antiphase boundaries are present in both regions as well. The only difference between the centre and the edges of sample no. 2 involves microtwin bundles: in the center region, there are two microtwin bundles per micrometre of interface, extending up to 6 km in the GaAs film while on the edges, there is one bundle per micrometre with an extension of only one micrometre into the epitaxial layer. Mirrorlike GaAs films can be obtained on (100) Ge substrates of at least 1 in ( 1 in = 2.5 cni) in diameter by increasing 6 to 0.2 cm and by injecting water vapor in the reactor only when Ti reached 650°C: the other deposition parameters reniain the sanie as for sample no. 2. In these conditions, th...

Evidence Provided by SIMS and EXAFS, of Ge Microclusters in GaAs Epitaxial Layers Obtained on Ge by CSVT

“…A review of the previous literature on the same topic is given in Ref. With this technique, GaAs layers are found n-type, with a charge density (ND-NA) between 10 TM and 10 TM cm-% The same large charge density was also measured in the present case (8). With this technique, GaAs layers are found n-type, with a charge density (ND-NA) between 10 TM and 10 TM cm-% The same large charge density was also measured in the present case (8).…”

“…Except for a very few misoriented planes, usually appearing at random, the pole figures of the GaAs layer are the same as the corresponding pole figures of bulk (100) GaAs (8). {311} and {111} pole figures have been recorded.…”

“…The raw SOI substrates have been evaluated by ellipsometry (3, 4), spreading resistance (5), four-point probing (6), low-temperature transport (7,8), Hall effect spectroscopy (9), and photo-induced current transient spectroscopy (PICTS) The raw SOI substrates have been evaluated by ellipsometry (3, 4), spreading resistance (5), four-point probing (6), low-temperature transport (7,8), Hall effect spectroscopy (9), and photo-induced current transient spectroscopy (PICTS)…”

“…As a first step toward the production of GaAs solar cells on Ge, GaAs epitaxial layers have been obtained by CSVT on Ge substrates (8). A review of the previous literature on the same topic is given in Ref.…”

“…ameter range(34). The ratio of the total number[8] of Ge bonds engaged in the coordination with other atoms to the total number of Ge bond available in a 5 Ge atom structure[20] is r = 0.4. The ratio of the total number[8] of Ge bonds engaged in the coordination with other atoms to the total number of Ge bond available in a 5 Ge atom structure[20] is r = 0.4.…”