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The collector characteristics of a transistor laser (TL) with a single base quantum-well (QW) showing the region of gain “compression” above the threshold base current for the ground state laser and the transition from the ground to the first excited state laser at base current .
(Color online) The differential current gain, , of the TL of Fig. 1 identifying the regions of “compression” with the abrupt reduction in at and . Similar behavior is obtained at other biases .
(Color online) The calculated optical gain and the corresponding differential gain of a QW TL for the ground state and first excited state transitions assuming an ideal “staircaselike” density of states. The base threshold current is denoted by , while denotes the range of base current where both ground and first excited state transitions are observed. The threshold gain is shown as .
(Color online) The differential laser output, , extracted from the characteristics of the TL of Fig. 1 plotted assuming the mirror loss, , and external quantum efficiency, . This is compared to the calculated values of obtained from Eqs. (4) and (6). The abrupt increase at reflects the “staircaselike” density of states of the single QW as the laser makes the transition from the ground to first excited state.
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