Data and analysis are presented showing that heavy p-type stochastic doping of the base barrier region of an n-p-n quantum-well (QW) light-emitting transistor (LET) or transistor laser (TL), the acceptors within tunneling range of the QW and perturbing the QW, enhances the LET or TL base recombination (base current) and the device speed (bandwidth). A relationship between the spontaneous recombination rate (1/lifetime, 1/τ) and the base current density is derived by considering (stochastic-doping) modified rate balance equations involving the spontaneous, A21, and stimulated recombination coefficients, B21=B12, and is verified with experimental optical microwave modulation (bandwidth) data obtained on QW-LETs.

We report for an n-InGaP/p-AlGaAs/i-InGaAs-QW/n-GaAs heterojunction bipolar light emitting transistor (HBLET) the record spontaneous optical-signal bandwidth, at −3 dB, of 1.8–4.3 GHz (corresponding to an effective carrier recombination lifetime of 37 ps). Besides the improved circuit matching of three-terminal device operation, the extension in performance is achieved by the lateral reduction in the emitter aperture size DA from 13 to 5 μm to provide higher injection current densities and better confinement of the radiative recombination in the base region. By reducing the carrier loss to lateral extrinsic recombination, we obtain with HBLETs higher current gains β(=ΔIC/ΔIB>30) and simultaneously >4 GHz optical bandwidths.

A tunnel junction is incorporated at the collector of a transistor laser to provide an effective method for voltage-controlled modulation via internal (intracavity) Franz–Keldysh photon-assisted tunneling. Electrical-optical signal mixing above threshold is made possible by the nonlinear coupling of the optical field to the base emitter-to-collector carrier transport and the base-to-collector electron tunneling. Microwave signal mixing with a common-emitter tunnel junction transistor laser is demonstrated with a pair of input sinusoidal signals: one (f1=2.0 GHz) at the base using current modulation and the other (f2=2.1 GHz) at the collector using voltage modulation, producing an optical output with harmonics of up to (4f1+7f2)=22.7 GHz, despite being limited by amplifier bandwidth.

We demonstrate a quantum-well base heterojunction bipolar light emitting transistor (HBLET) operating in the common collector configuration with a 3 dB optical response bandwidth f3 dB of 4.3 GHz. The HBLET has a current gain, β (=|ΔIC/ΔIB|) as high as 30, and can be operated as a three-port device to provide simultaneously an optical and electrical output with gain. The f3 dB of 4.3 GHz corresponds to an effective carrier recombination lifetime of 37 ps, and shows that “fast” spontaneous recombination can be harnessed for high-speed modulation.

We show experimentally and analytically that fast spontaneous recombination lifetime, τB,spon, leads to resonance-free frequency response in semiconductor lasers, and as a consequence higher speed operation. Faster τB,spon is obtained by a reverse-bias collector field pinning and tilting a dynamic (removable) charge population in a thin base (τt∼ps), allowing only “fast” recombination. We show resonance-free optical response on a prototype transistor laser (TL) with τB,spon∼29 ps. Based on the TL, a resonance-free tilted-charge diode laser, is demonstrated with a 10.3 Gb/s “clean open-eye” signal achieved with a −3 dB bandwidth device of only 5.6 GHz.

A transistor laser with a tunnel junction collector is demonstrated. Its optical output is sensitive to third terminal voltage control owing to the electron tunneling (photon-assisted or not assisted) from the base to collector, which acts in further support of resupply of holes for recombination in addition to the usual base Ohmic current, I(B). Collector tunneling enhances laser operation even under a weak collector junction field and quenches it under a strong reverse-biased field. The sensitivity of the tunnel junction transistor laser to voltage control enables the tunnel junction transistor laser to be directly modulated by both current and voltage control.

We demonstrate a higher speed form of light emitting diode (LED), an asymmetrical two-junction tilted-charge LED, utilizing an n-type buried “drain” layer beneath the p-type “base” quantum-well (carrier and photon) active region. The drain layer tilts and pins the charge in the manner of a heterojunction bipolar light emitting transistor (HBLET), selecting and allowing only “fast” recombination (recombination lifetime τB of the order of base transit time τt). The tilted-charge LED, simple in design and construction, is capable of operation at low current in spontaneous recombination at a 7 GHz bandwidth or even higher with more refinement.

We report the improvement, from 10.5to22GHz, in the optical modulation bandwidth of a quantum-well (QW) heterojunction bipolar transistor laser (TL) by the use of an ac auxiliary base signal. Because of the three-terminal form of the TL, an auxiliary signal can be used to peak the photon output, e.g., stimulated recombination which simultaneously reduces the operating current gain, β(=ICO∕IBO), and increases the laser differential gain. A shorter effective base carrier lifetime, τ, owing to the increased QW recombination rate (stimulated recombination), enhanced carrier transport to the “faster” QW collector (reduced β) and differential gain, result in a higher 3dB bandwidth (f3dB=1∕2πτ).

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.

Data are presented on the transistor laser light-output (L I-V ) as a function of base current and the collector-to-emitter voltage (V CE ) revealing sensitive fine structure that can, with suitable bias, be exploited for signal switching and mixing. The output light intensity versus current-voltage characteristics (L I-V ) and the fine structure in the L I-V characteristics are related to the change in laser operation from the ground state to the first excited state of the quantum well incorporated in the transistor base, laser mode changes, or shift from spontaneous to stimulated emission (or the reverse). The region of stimulated recombination and its boundary are or particular interest. The concept of the voltage-driven switching of a transistor laser employing the Franz-Keldysh photon-assisted process to shift the operation from stimulated (high coherent optical field) to spontaneous (lower incoherent field) is demonstrated

A quantum well (QW) transistor laser with the capability of high current density, a collector current ensuring minimal operational change (beyond laser threshold) in base QW carrier population, a favorable long narrow emitter laser geometry, and built-in base-collector Franz-Keldysh absorption (with IE+IB+IC=0), is measured for chirp-related behavior. A relatively low transistor laser linewidth enhancement factor αe∼0.7 is obtained despite the resolution limitations of the measurement apparatus.

Measured modal gain spectra of the tunneling injection InP quantum-dot (QD) laser with and without an external feedback are presented to experimentally demonstrate the polarization-dependent photon-mediated carrier redistribution in the tunneling injection QD laser. The peak gain wavelength in the transverse-electric gain narrowing spectra near threshold follows the external feedback wavelength. This indicates that the carrier redistribution in the QD-coupled-quantum well structure is determined by the spectral distribution of the stimulated emission, which can be controlled by external grating.

The electrical and optical characteristics of high-gain, small-area InGaN/GaN heterojunction bipolar transistors (HBTs) grown by metal-organic chemical vapor deposition on sapphire substrate are reported. The common-emitter current-voltage characteristics of a 3 x 10 mu m(2) emitter device demonstrates a current gain beta=Delta I-C/Delta I-B=49 at 3 mA and breakdown voltage, BVCEO>70 V. The radiative recombination spectrum of a large area 100 x 100 mu m(2) emitter HBT is measured, showing a peak at 387 nm and a full width at half maximum of 47 nm. A 1 kHz modulation input is applied to the HBT and both the optical and electrical outputs of a large area device is demonstrated. (c) 2007 American Institute of Physics.

The authors report the calculation of the minority carrier distribution in the base region of the transistor laser (TL) employing the relevant continuity equations and experimental carrier lifetimes, spontaneous and stimulated, extracted from the transistor I-V characteristics. A charge control model of the TL is developed, consistent with the short recombination lifetime of the quantum-well base (which competes with the short emitter-to-collector transit time). The absence of carrier-photon resonance of a TL is demonstrated with the 3dB bandwidth (IB∕IB,th=1.5) estimated to be 30GHz for a 400μm long laser cavity length and 70GHz for a 150μm cavity.

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.

We investigate a tunneling injection InP quantum-dot (QD) laser theoretically and experimentally. The device consists of a single compressively strained InP QD layer coupled closely to two tensile strained InGaP quantum wells (QWs). While most tensile strained QW lasers in this wavelength (red) range lase in the transverse-magnetic (TM) polarization, our QD laser lases in the transverse-electric (TE) polarization from the first excited state of the compressively strained QDs, which is coupled to the ground state of the tensile-strained InGaP QWs. When we measure TE and TM modal gain spectra, a typical QW gain evolution behavior is observed at low injection currents, which can be theoretically explained by the quasi-equilibrium of carrier distribution. When the injection current is increased near threshold, a TE gain narrowing and a simultaneous TM gain pinning are observed in the measured modal gain spectra, which cannot be explained via the quasi-equilibrium model. We propose a polarization-dependent photon-mediated carrier re-distribution in the QD-coupled-QW structure to explain this TE and TM gain evolution behavior. When the injection current is just below threshold, the strong carrier depletion via stimulated emission due to coupling between the InP QD and InGaP QW states plays an important role in carrier re-distribution, which depends on the optical transition energy and polarization. This polarization-dependent photon-mediated carrier re-distribution explains the TE gain narrowing and TM gain pinning behavior. To quantitatively demonstrate the photon-mediated carrier re-distribution near the threshold current, a set of coupled rate equations are solved taking into account the polarization-dependent stimulated emission processes. The calculated polarization power ratio based on the coupled rate equations explains the experimental observations.

A quantum well (160Å) transistor laser with a 400μm cavity length that achieves the large 3dB modulation bandwidth of 13.5GHz is described. The fast base recombination (transport determined, τBL<10ps) permits improvement of the carrier-photon damping ratio (>1∕2), resulting in a resonant peak magnitude of unity and consequently a resonance frequency of ∼0GHz (no peak) in the small-signal response. Quantum well band filling and bandwidth saturation are observed on the ground state (λ=1000nm), and increase with operation on the first excited state (λ=980nm).