The thermal properties of gallium arsenide laser structures

The development of high-power junction lasers has resulted in the development at many laboratories of laser structures which will enable devices to operate at high mean power or continuously at the highest possible temperature. However, little attention has been paid to the measurement of the thermal properties of the resulting structures. Although CW operation does not, in general, give the maximum mean power from a device, continuous operation at elevated temperatures is a convenient development aim and it is shown that this can be predicted on the basis of two conditions: 1)
\gammaI_{0}v\theta/T_{0} < 0.15
if joule heating is small, or 2)
I_{0}^{2}R\theta/T_{0} < 0.067
if joule heating dominates the device dissipation, where I
0
threshold current at the ambient temperature T
0
V
junction voltage 0 thermal impedance of the device
R
effective ohmic resistance of the device 1 - γ device quantum efficiency. Various methods of measuring the thermal impedance θ have been devised and are considered in detail. These methods involve observations of spectra or threshold under various operating conditions and give results which are in good mutual agreement. It is suggested that the thermal properties of a device can conveniently be described in terms of two figures of merit given by
I_{0}V\theta_{\gamma}
and
I_{0}^{2}R\theta
.