Performance of multiquantum barriers in bulk double heterostructure visible laser diodes as a function of temperature

The validity of the claim that multiquantum barriers (MQBs) improve the performance of visible laser diodes by virtue of a virtual barrier height increase over the bulk barrier height was investigated by designing three types of bulk active region double heterostructure Ga_0.5In_0.5P/(Al_0.4Ga_0.6)_0.5In_0.5P laser diodes. The first was used as a reference while the remaining lasers included an optimised and non-optimised MQB structure respectively. The optimised MQB design is intended to produce a virtual barrier height increase of 75meV while the non-optimised design is expected to be identical to the bulk reference laser. The active region of each laser was adjusted to keep the total optical confinement the same for all three structures. The threshold current for all three laser types was measured under pulsed conditions as a function of temperature from 70K to 353K. It is noted that below 190K all three lasers behave identically and the threshold current increases linearly with temperature. As the temperature increases, thermal leakage of carriers becomes more significant and the threshold current for the bulk reference laser increases faster than both of the MQB lasers. Against expectation the non-optimised MQB outperforms the bulk laser, indicating that even the non-optimised MQB reduces the threshold current. Above room temperature the disparity between the bulk and the MQB lasers enlarges, while the non-optimised MQB laser performs equally as well as the optimised MQB laser.