ABSTRACT
There exist few lattice matched semiconductor hetero systems, such as GaAs/AlGaAs in nature. Any epitaxy technique could not avoid producing lattice mismatched heterostructures. Lattice-mismatched growth has been widely investigated for a variety of material systems in the recent two decades, because of their attractive properties. Applications for lattice-mismatched films can be divided into two kinds: (i) utilization of the strained layer itself; (ii) using a common substrate as a template for the growth of relaxed layers. Typical of the first application is the GaAs/InGaAs/AlGaAs pseudomorphic high electron mobility transitor (PHEMT). In this case, a strained layer of InGaAs with low Incomposition is induced as an electron channel for electron mobility enhancement, because InAs has a lower effective mass and much higher electron mobility, compared with GaAs. The layer thickness of InGaAs is kept below the critical thickness to avoid the formation of misfit dislocations which degrade the electrical and optical properties of carriers. Due to the limited thickness and strain required for coherently strained growth, the design options for electronics, optoelectronics and photonics applications are restricted.
