Quantum-well Transistor Laser Research Articles

Tunneling modulation of a quantum-well transistor laser

Different than the Bardeen and Brattain transistor (1947) with the current gain depending on the ratio of the base carrier spontaneous recombination lifetime to the emitter-collector transit time, the Feng and Holonyak transistor laser current gain depends upon the base electron-hole (e-h) stimulated recombination, the base dielectric relaxation transport, and the collector stimulated tunneling. For the n-p-n transistor laser tunneling operation, the electron–hole pairs are generated at the collector junction under the influence of intra-cavity photon-assisted tunneling, with electrons drifting to the collector and holes drifting to the base. The excess charge in the base lowers the emitter junction energy barrier, allowing emitter electron injection into the base and satisfying charge neutrality via base dielectric relaxation transport (∼femtoseconds). The excess electrons near the collector junction undergo stimulated recombination at the base quantum-well or transport to the collector, thus supporting tunneling current amplification and optical modulation of the transistor laser.

Voltage and Current Modulation at 20 Gb/s of a Transistor Laser at Room Temperature

Data are presented showing open-eye 20-Gb/s transmission for a quantum-well transistor laser operating at room temperature (25°C). The fast spontaneous recombination lifetime (~ 30 ps) in the base region results in a resonance-free frequency response allowing demonstration of 20-Gb/s transmission with an I/ITH=3. It is shown that higher temperature hastens the transition to the first excited state and improves bandwidth and eye-opening at low bias levels (I/ITH=2). In addition, room temperature 20-Gb/s transmission through voltage modulation of a transistor laser via intracavity photon-assisted tunneling in the base-collector junction is reported.

Bandfilling and photon-assisted tunneling in a quantum-well transistor laser

Data and a phenomenological model for quantum-well (QW) transistor laser operation are presented showing, via the three-port input-output (electrical and optical) characteristics, the strong QW to collector coupling and the influence of bandfilling (QW states, Δhν recombination radiation, sensitivity of Eλ0→Eλ1,λ0→λ1,λ0>λ1) on base-to-collector photon-assisted tunneling and laser operation. Transistor (electrical) and laser (optical) operation are locked and “slide” up and down as a function of base current (IB), collector-base voltage (VBC or VCE), and the influence of QW bandfilling (with increased sensitivity at Eλ0→Eλ1) on photon-assisted base-collector tunneling.

Temperature dependence of a high-performance narrow-stripe (1 μm) single quantum-well transistor laser

Data are presented on the thermal behavior of a high performance 1 μm wide stripe quantum-well (QW) transistor laser in continuous-wave single-mode operation up to 40 °C, multimode to 55 °C. The electrical and optical outputs of the TL are found to be complementary across temperature, directly correlated with the spontaneous and stimulated radiative recombination process. The QW transistor laser operates on two states, lower and upper, at two characteristic temperatures, T0 (ITH=I0 exp(T/T0)). On the lower state transition, T00=40 K, and on the upper state, T01=70 K, the difference in performance and speed (bandwidth) connected directly to the different recombination lifetimes on each state and the confining barrier heights of the lower |0⟩ and upper state |1⟩.

Collector characteristics and the differential optical gain of a quantum-well transistor laser

The collector electrical characteristics (I-V) of a transistor laser (TL) manifest directly the transport and recombination dynamics of the vital quantum-well (QW) base region, including as described here QW recombination state changes. By employing the continuity equations and an extension of the classic charge control model, we extract from the dc I-V characteristics the differential optical gain of a single QW TL showing the QW state changes. The results agree in form with calculations employing Fermi’s golden rule and the “staircaselike” density of states of a QW.

Photon-assisted breakdown, negative resistance, and switching in a quantum-well transistor laser

Data are presented on the transistor laser with collector bias and photon-assisted tunneling causing, under the constraints IE+IB+IC=0 (α=ΔIC∕ΔIE) and α→1, breakdown and negative resistance effects in the IC-VCE characteristics. Collector bias, aided by photon-assisted tunneling (Franz—Keldysh absorption), supplies holes to the n-p-n transistor base by tunneling escape of electrons (ΔIB=0), “feeding” quantum-well recombination radiation (generation and regeneration, ΔIE=ΔIC=ΔIhv) and yielding the negative resistance/switching condition α→1 (α=ΔIC∕ΔIE, ΔIC=ΔIE, ΔIB=0, IE+IB+IC=0), and, as a consequence, corners, negative resistance, switching, vertical collector current (ΔVCE≈0), spectral change, and mode hopping effects in the IC-VCE characteristics.