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 multi-quantum-well (SMQW) lasers was simulated for improving their performance. The simulations were carried out using the device simulator WIAS-TeSCA based on a drift-diffusion model which is self-consistently coupled to a heat-flow equation (see ) 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 edge-emitting ridge waveguide (RW) laser.
The most important part of
cross section is shown in Figure 1, the simulated
P-I characteristic in Figure 2.
Besides RW lasers we investigated also buried heterostructure lasers in
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).
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 Hn
is seen in Figure 4.
An excellent fit of Hn can be obtained
according to the formula
The last factor in (1) is well known from rate equation models
The second factor is a low-pass filter while the first one describes some
time delay. Both terms are
due to parasitic effects,
especially to the drift-diffusion transport
through the device (see , too). The result of the fit
is demonstrated in Figure 3.
The extracted parameters
are presented in a more suitable form in Figure 5.
is also shown there
solves the equation .Let us note that a fit without using the parasitic terms gives
The second method is a current-driven transient simulation where a short
rectangular pulse is added to the injection current
( mA, ).
computes corresponding variations
of the output power which are seen in the
right-hand 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