Abstract
To suppress bipolar population and hence electron–hole
recombination outside quantum dots (QDs), tunneling-injection of electrons
and holes into QDs from two separate quantum wells was proposed earlier.
Close-to-ideal operating characteristics were predicted for such a double
tunneling-injection (DTI) laser. In the Stranski–Krastanow growth
mode, a two-dimensional wetting layer (WL) is initially grown followed by
the formation of QDs. Due to thermal escape of carriers from QDs, there will
be bipolar population and hence electron–hole recombination in the
WL, even in a DTI structure. In this work, the light–current
characteristic (LCC) of a DTI QD laser is studied in the presence of the WL.
Since the opposite sides of a DTI structure are only connected by the
current paths through QDs and the WL is located in the n-side of the
structure, the only source of holes for the WL is provided by QDs. It is
shown that, due to the zero-dimensional nature of QDs, the rate of the hole
supply to the WL remains limited with increasing injection current. For this
reason, as in the other parts of the structure outside QDs (quantum wells
and optical confinement layer), the parasitic electron–hole
recombination remains restricted in the WL. As a result, even in the
presence of the WL, the LCC of a DTI QD laser becomes increasingly linear at
high injection currents, which is a further demonstration of the potential
of such a laser for high-power operation.
© 2009 IEEE
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