Stimulated emission related anomalous change of electrical parameters at threshold in GaN-based laser diodes

Abstract

We report the stimulated emission related anomalous behavior of electrical parameters in GaN-based laser diodes based on both experiments and self-consistent calculations. In particular, the separation of quasi-Fermi levels of electrons and holes across active region shows a drop (or “pinning”) in threshold region, followed by an increase with current. The start and end points correspond to the two kink points of the first derivative of the optical output power-current (P-I) curve. This abnormal change of electrical parameters always satisfies the need of sufficient carriers for stimulated emission in the process of transition to lasing as well as lasing enhancement.

Redefinition the quasi-Fermi energy levels separation of electrons and holes inside and outside quantum wells of GaN based multi-quantum-well semiconductor laser diodes

“…This saturation effect seems to be consistent with the above scholars' results and the current laser theory. However, for wide bandgap GaN-based LDs, V j experiences a drop (or 'pinning') in the threshold region, and then increases under higher current injection [1][2][3]. Experimental results are perfectly consistent the self-consistent calculations [1][2][3].…”

“…However, for wide bandgap GaN-based LDs, V j experiences a drop (or 'pinning') in the threshold region, and then increases under higher current injection [1][2][3]. Experimental results are perfectly consistent the self-consistent calculations [1][2][3]. It indicates that the abnormal characteristics of the junction voltage after the threshold of GaN LDs should be certain; however, its corresponding physical mechanism needs to be further explored.…”

“…They concluded that for all real LDs, threshold region should be adopted instead of a threshold point to describe the electrical and luminescent properties. In this region, the sudden changes of electrical characteristics between narrow and wide bang-gap multiquantum-well (MQW) LDs are opposite [1][2][3], as shown in figure 1. Especially, for narrow band gap LDs, the V j jumps abruptly in threshold region then saturates [27].…”

Impact of quantum dots on III-nitride lasers: a theoretical calculation of threshold current densities

“…For example, InGaN quantum well (QW) lasers have typical J th values of 1-4 kA cm −2 , or even higher. [15][16][17][18][19] Indeed, the imperfections in crystal growth and electrode fabrication could play important roles in the large J th values, whereas other factors in III-nitrides should also be taken into accounts, i.e., the large effective-masses of carriers ( m c * in conduction bands and m v * in valence bands) and their large asymmetry (m m 1 v c * * > / ). As known, under parabolic approximation assumptions for band structures, the density of states (ρ(E)) in three dimensional (3D) bulks ( m ) increase with effective-masses of carriers.…”

The design criteria of hybrid waveguides using semiconductor gain to compensate the metal loss towards nano-scale lasers with high plasmonicity

“…1 obtained from previous publications may be from the kink behaviour of the threshold region in the plot of output power versus excited-power/injected current, because the lasing threshold could be manifested as the start or end point of kink region or even points between them. [22][23][24] The discussion on Fig. 1 indicates that it would be extremely difficult to generate an ideal case of coherent plasmon.…”