  Computer simulations with Synopsys' Sentaurus TCAD of opto-electrical
characteristics of separate-confinement heterostructure laser based on AlGaAs
are used as an example to study the role of the width and depth of Quantum Well
(QW) active region on laser characteristics, I-V and I-L, below and above the
lasing threshold. The device properties depend on both, the number of bound QW
states and on closeness of the highest bound states to conduction or valence
band offset. The lasing action may not exist at certain widths or hights of QW,
the threshold current is a discontinuous function of these parameters. The
effects are more pronounced at low temperatures. Discontinuities in
characteristics may be observed at certain conditions in temperature
dependencies of laser parameters.
