S.G. Li

Measurements of I–V characteristics in InAs/InP quantum dot laser diode

The current–voltage (I–V) characteristics are reported of an InAs/InP quantum dot laser diode operating under the continuous wave mode. The laser diode emits a wavelength of 1.55 µm at a temperature of 293 K. The maximum operation temperature reaches 343 K. As the injection current is increased, a nonlinear relationship between ln(I) (where I is the injection current) and applied voltage is observed. When the operating temperature is increased, the forward voltage and turn-on voltages decrease. The voltage is found to drop linearly with operation temperature. However, the temperature efficiency of forward voltage (slope: ) is nonlinear with the applied current. In the injection current range from 5 to 400 mA, the temperature efficiency of forward voltage decreases from −1.27 mV/K to −6.68 mV/K. The dVF /dT shows a linearity with the function ln(I), which agrees well with the simplified Shockley equations. In addition, the band gap of the laser diode is obtained by fitting the forward voltage with operating temperature at low injection current.

Fabrication of narrow-striped InAs/GaAs quantum dot laser with wet etching technique

An InAs/GaAs quantum dot laser, fabricated with a narrow-striped width of 6 μm by a wet etching technique, is reported. The etching solutions are composed of three components, i.e. phosphoric acid, hydrogen peroxide, and deionized water. We observed that the unavoidable undercutting was changed with the ratio of etching solution in the GaAs materials. By taking a suitable ratio of etching solution, good performance of quantum dot laser with a size of 6 μm × 700 μm was achieved for fabrication at room temperature. Under continuous wave mode, the lasing wavelength exhibited a single mode, which is located in the region of 1051 nm. In contrast, multimode lasing with a series of non-lasing gaps appeared and the spectra were gradually broadened to the high energy side by increasing the injection current. The laser has one facet power more than 22 mW, with a slope efficiency of 140 mW/A, just a little above threshold current.

A Novel Method to Measure the Internal Quantum Efficiency and Optical Loss of Laser Diodes

We present a novel method to characterize the internal quantum efficiency and internal optical loss of semiconductor lasers. Its basic concept is studying the dependence of the external quantum efficiency on the mirror reflectivity. This method is very different from the conventional one, which focuses on the external quantum efficiency as a function of cavity length. Our method has great advantages, such as the capability of measuring the internal quantum efficiency and optical loss of a single laser diode, which is intrinsically impossible by the conventional method.