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Cooperation with: F. Fidorra, M. Krieg (MergeOptics GmbH, Berlin)
Supported by: MergeOptics GmbH
Description: In cooperation with the company MergeOptics GmbH the electrical, thermal, optical and dynamical behavior of strained multiquantumwell (SMQW) lasers was simulated for improving their performance. The simulations were carried out using the device simulator WIASTeSCA based on a driftdiffusion model which is selfconsistently coupled to a heatflow equation (see [1]) and to equations for the optical field. The main goal was the optimization of the modulation response of such lasers. For this purpose details of the structure (e.g., number of quantum wells, thickness of waveguides) and the doping were varied.
Methods and results are demonstrated here
for some fictive edgeemitting ridge waveguide (RW) laser.
The most important part of
its transverse
cross section is shown in Figure 1, the simulated
PI characteristic in Figure 2.
Besides RW lasers we investigated also buried heterostructure lasers in
more detail.
We describe two methods for the calculation of the modulation response.
The first one
is the AC analysis (small signal analysis in the frequency domain).
Here WIASTeSCA
computes complex amplitudes ,
corresponding to a small harmonic modulation of the bias
voltage with angular frequency and amplitude
( mV). The complex
response function is then given by
, or in a
normalized form by . The squared modulus of H_{n}
is seen in Figure 4.
An excellent fit of H_{n} can be obtained
according to the formula
(1) 

The last factor in (1) is well known from rate equation models
(see [2]).
The second factor is a lowpass filter while the first one describes some
time delay. Both terms are
due to parasitic effects,
especially to the driftdiffusion transport
through the device (see [3], too). The result of the fit
is demonstrated in Figure 3.
The extracted parameters
,
, and
are presented in a more suitable form in Figure 5.
The frequency
is also shown there
where
solves the equation .Let us note that a fit without using the parasitic terms gives
insufficient results.

The second method is a currentdriven transient simulation where a short
rectangular pulse is added to the injection current
( mA, ).
WIASTeSCA
computes corresponding variations
of the output power which are seen in the
righthand side of Figure 4 for
(to enhance clearness the result for
I=75 mA was omitted here). Corresponding to (1) the
functions were fitted according to the formula
(2) 
References:



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