Derivative measurements of the current-voltage characteristics of double-heterostructure injection lasers

Measurements of the electrical characteristics of double-heterostructure (DH) stripe-geometry AlGaAs junction lasers are reported. We show that the electrical characteristics of these lasers are adequately represented by a resistor in series with a p-n junction characterized by a classical diode equation,
I = I_{s} [\exp (q V_{j}/\etakT) - 1]
. Devices have been measured with almost ideal junction characteristics with both the saturation current, I
s
, and the exponential parameter, η, constant, while in other diodes both η and I
s
exhibit a strong current dependence. Measurement of the first derivative
dV/dI
and the product
IdV/dI
is shown to be an especially useful technique for electrical characterization, yielding accurate and direct determination of the series resistance, the exponential junction parameter, and the laser threshold current. The observation of lasing threshold from an electrical measurement, instead of from the more usual optical measurement, is discussed in terms of the saturation behavior of the junction voltage at and above threshold.