Gain characteristics of quantum dot injection lasers

Abstract

Gain characteristics of injection lasers based on self-organized quantum dots (QDs) were studied experimentally for two systems: InGaAs QDs in an AlGaAs matrix on a GaAs substrate and InAs QDs in an InGaAs matrix on an InP substrate. A ground-to-excited state transition was observed with increasing threshold gain. An empirical equation is proposed to fit the current density dependence of the QD gain. This fitting equation is shown to be valid for both the ground and excited state lasing in the systems under study in the 77-300 K temperature range. The effect of QD surface density on gain characteristics is calculated analytically.

Broadband Emission in Quantum-Dash Semiconductor Laser

“…At J > 1.5×J th , the bi-state lasing is noted. The simultaneous lasing from both E 0 and E 1 is attributed to the relatively slow carrier relaxation rate and population saturation in the ground state in low-dimensional quantum heterostructures (Zhukov et al, 1999). The transition from mono-state to bi-state lasing is marked with a slight kink in the L-I characteristics.…”

Optical Gain in GaInNAs and GaInNAsSb Quantum Wells

“…While the saturation value of the gain, g sat is not usually accessible experimentally due to the onset of gain from the next pair of sub-bands it does provide a measure of the maximum gain which a single pair of sub-bands can provide. In principle g sat can be determined by fitting an alternative expression to the g-J data, originally proposed for quantum dot systems [17] Peak local gain per well cm −1 Fig. 2.…”

Electronic Properties of InAs/GaAs Self-Assembled Quantum Dot Structures and Devices Studied by Photocurrent Spectroscopy

“…However, although impressive performances have been reported for self-assembled QD lasers [19] there is considerable evidence that the basic model gain is relatively small [20], probably as a result of the low fractional area occupancy of the dots. In this section we show how PC measurements can be used to determine the modal gain of a quantum dot laser and investigate the consequences for device performance of the low value found.…”

“…In the light of these considerations the relative values of gm a x m o d f o r a Q D a n d Q W l a s e r a r e r e a s o n a b l e . The small value determined for g m a x m o d i s c o m p a r a b l e t o t h e i n t e r n a l c a v i t y loss (αi), which typically has a value in the range of ~ 2-10 cm -1 [20], and thus lasing on the ground state transition may be diffIcult to achieve. Such lasing is desirable, as carriers in the corresponding dot states are the most strongly confined, hence minimising thermal carrier loss from the dots and resulting in the optimum temperature performance.…”

“…Unlike the technique used in Ref. [20], which requires the measurement of a large number of laser devices, the. present technique requires the measurement of a single, more easily fabricated mesa device.…”