The critical thickness, characteristic for the lattice-mismatch parameter, plays a key role in the growth of strain layers. The driving force for the 2D-3D transition can be minimized by slowing the relaxation of misfit strain. As a result - the relatively smooth layer is deposited at lower temperature for the optimal growth rate. The quality of the InGaAs- and AlAs-strained layers deposited on InP substrate have been examined by the XRD, AFM and SIMS methods. Atomic force microscopy allows to observe 3D growth mode even for very thin layers. Relatively strong relaxation effects are recognized by surface roughness. Two-dimensional diffraction measurement is a much more sensitive tool for the estimation of relaxation degree. The observations results were applied in the heterostructure barrier varactor (HBV) diode. In order to minimize the conduction current through HBV two materials with different design of the barriers were studied: one heterostructure with three homogeneous lattice matched barriers consisting of 20 nm Al0.48In0.52As and another one with strained step-like barriers consisting of 5 nm Al0.48In0.52As, 3 nm AIAs and 5 nm Al0.48In0.52As. We found that the use of strained step-like barriers results in a much lower conduction current. For current density less than or equal to 0.1 muA/mum(2). the maximum voltage was about 10V per barrier, which is to our knowledge more than for any reported HBV material.