Temperature dependence of threshold current in (GaAl)as double-heterostructure lasers with emission wavelengths of 0.74-0.9µm

The threshold-current variation with temperature has been measured for Ga
1-x
Al
x
As double-heterostructure (DH) lasers with AlAs mole fraction in the active layer
x
of 0.08 and 0.2, and with several heterojunction step heights
\Deltax
. The threshold-temperature coefficient J
th
(350 K)/J
th
(300 K), which generally increases with decreasing
\Deltax
, is found to be larger for
x = 0.2
than that for
x = 0.08
at the same value of
\Deltax
, and also to be larger for the lasers with smaller effective electron diffusion length in the
P
cladding layer, in the case of
x = 0.2
. These characteristics are well explained by a model of carrier leakage due to unconfined carriers in the active layer. It is confirmed by a good fit of the experimental results with the calculated values that the electron leakage in the
\Gamma
conduction band of the
P
cladding layer dominates for
x \leq 0.1
, but the hole leakage in the
N
cladding layer increases with
x
and becomes comparable in magnitude with the electron leakage at
x \sim 0.2
.