|
Low pressure MOVPE in a horizontal reactor has proven to be capable of yielding uniform lnP, GalnAs and GalnAsP layers /1 , 2/. However, the complexity of some devices as MOW lasers and HEMTs require even further improve — ment in thickness and compositional uniformity. This can be achieved by using the technique of substrate rotation to overcome gas phase depletion problems and geometry related non uniformities. Techniques for the pratical realization of such systems using a mechanical drive have been described earlier /3/. However, the technical solution for substrate rotation, using mechanical feed throughs was only applied to small, laboratory scale systems. In this paper we will discuss the use of the new 'gas foil rotation' technology for growth in a low pressure reactor. In this technique the wafer holder is floating on a foil of high purity hydrogen. Since the hydrogen is forced to flow with a circular component, the plate with the substrate is put into rotational motion /4, 5/. lnP, GalnAs and GalnAsP layers grown in a single wafer reactor on 2' substrates applying this substrate rotation show film thickness variations less than 2% over the entire wafer. Resistivity measurements on doped binary layers showed variations of less than 2%. The lattice mismatch variations of ternary and quaternary layers was below 5x104. The electrical properties of GalnAs and nP as residual carrier concentration and electron mobility in undo— ped layers were identical to those measured on reference layers grown in the same reactor on a static susceptor. Growth parameters had not to be modified when using this technique. The gas foil rotation assembly does not require mechanical drive parts, feed through etc., and thus does not generate particles; it can easily replace the standard static susceptor with only minor changes in the gas supply system. The method has also been applied in multiwafer reactors, where the wafers rotate in 'planetary" motion. Similar results have been obtained in a horizontal reactor with 5 wafers rotating in planetary motion. The growth of GaAs/AlGaAs heterostructures and InGaAs with outstanding film properties and high requirements on film homogeneities such as HEMTs /1 , 2/ has been demonstrated in an atmospheric pressure reactor designed for 7 wafers rotating in planetary motion in a radialsymmetric horizontal flow system.
|
