Effect of gas switching on InP/InGaAs interfaces during CBE growth

The InP/InGaAs material system has several beneficial material properties which enable the development of high performance optical and electrical devices. However, high quality epitaxial layers with abrupt interfaces are necessary to attain the performance predicted. Several growth techniques, including metalorganic vapor phase epitaxy (MOVPE), chemical beam epitaxy (CBE), and gas source molecular-beam epitaxy (GSMBE), have been used to grow high quality layers with varying success in achieving abrupt interfaces.([1,2,3]) The difficulty in realizing abrupt interfaces arises from the As-to-P or P-to-As exchange process that occurs at heterointerfaces during the switching of the group V species. The presence of significant levels of residual As or P can degrade the interface due to the high incorporation efficiency of these molecules on the opposite terminated surface.([4]) In order to reduce residual levels of As or P, high pumping speeds, close-coupled run/vent switching, and separate hydride crackers may be necessary. ([5]) An added concern during CBE growth is the presence of residual group III molecules which can form unwanted transition layers at interfaces during subsequent growth. Formation of the poor interfaces can lead to both an increased difficulty in the fabrication of devices, if thick interfacial layers are present, and degradation of device performance due to scattering from rough interfaces. With the use of an optimized switching scheme the formation of these interfacial layers can be minimized. Several researchers have investigated the effect of switching on interfaces. A combination of growth/group III pauses as well as group V pauses, followed by the introduction of the opposite group V source prior to growth have been used.([2,3,6]) Researchers have shown varying degrees of success in reducing the extent of the interface layers, though interface layers on the order of 2-3 monolayers still remain. Tsang, et. al., has reported the best results in terms of low-temperature photoluminescence data, however, no information is available on the switching scheme used.([1]) In this paper, the effect of a simple gas switching sequence on interface abruptness during CBE growth is studied using double crystal x-ray diffraction (DCXRD), photoluminescence (PL), and scanning tunneling microscopy (STM). Optimization of the switching sequence produces monolayer abruptness for both the InP/InGaAs and the InGaAs/InP interfaces.