Transistor Laser Research Articles

Effect of the energy barrier in the base of the transistor laser on the recombination lifetime

Data are presented to quantify the effect of the conduction band energy barrier (ΔEC,B) in the base region of the transistor laser on the minority carrier transport dynamics, recombination lifetime in the base region, and frequency response of the device. A greater ΔEC,B results in lower transistor current gain (β) and higher optical output power, indicating increased carrier confinement and recombination in the base. For a device with ΔEC,B = 41 meV, the measured bias-dependent optical frequency response and subsequent data fitting yield a short recombination lifetime of 30 ps in the base and a small resonance peak of 1.5 dB. A device with ΔEC,B = 82 meV exhibits a longer recombination lifetime of 70 ps and a larger resonance peak of 4 dB.

Microwave-Photonic Links Based on Transistor-Lasers: Small-Signal Gain Analysis

The link gain for a directly modulated microwave-photonic link based on a transistor-laser (TL) is derived by making use of signal flow graph techniques. In contrast to conventional laser diodes, the three-terminal TL introduces an extra microwave port for impedance tuning of link parameters. Gain contour simulations using a small-signal equivalent circuit model for the TL indicate the potential for increased link gain compared with links that are terminated in 50 Ω at all ports.

Spectral characteristics of a 1.3-µm npn-AlGaInAs/InP transistor laser under various operating conditions

Spectral characteristics of a 1.3-µm npn-AlGaInAs/InP transistor laser under various operating conditions

Lateral feeding design and selective oxidation process in vertical cavity transistor laser

Lateral feeding design and selective oxidation process in vertical cavity transistor lasers (oxide-VCTLs) are developed for improving spatial current and optical modes confinement to achieve low threshold operation. Oxide-VCTLs with oxide apertures of 6.4 × 7.4 μm2 and 4.5 × 5.6 μm2 deliver threshold of 1.3 and 1.6 mA, respectively. The smaller oxide-VCTL exhibits a larger mode spacing of 1.02 nm and achieves a better side-mode suppression ratio of 37 dB. The low threshold oxide-VCTL with a high quality factor (Q) cavity shows a gradual current gain (β) compression when the transistor base recombination shifts from spontaneous to coherent stimulated emission as compared with a sharp β compression previously reported in a high threshold edge-emitting transistor laser with a lower “Q” cavity.

Theoretical analysis on optoelectronic performances of long wavelength transistor lasers: base width variation effects

We investigate the base width variation effects on various optical and electrical characteristics of double heterostructure long wavelength transistor laser (DH-LWTL). Considering the device structure, the base region geometry of a LWTL significantly affects its optoelectronic performance. We derive theoretical approximation of optical confinement factor (OCF), where we study the relationship between the base width and the OCF. In order to analyze optoelectronic performance of the LWTL, however, we have to consider the optical loss in base region with intervalence band absorption as the main factor in our calculation approach. We show that both the OCF and the optical loss have opposite trends with base width variation. Transient parameters including resonance peak and frequency are also inspected for their dependence on the base width as well as doping concentration. According to our simulations, we expect a minimum threshold current density of $$4.38\, \hbox {KA/cm}^{2}$$ and a maximum cut-off frequency of 28.22 GHz for 38 nm and 305 nm base widths, respectively. A relatively fast process of “carrier extinction” is also anticipated for narrow enough bases.

The Transistor Laser: Theory and Experiment

The quantum-well (QW) heterojunction bipolar transistor (HBT) laser [the transistor laser (TL)], inherently a fast switching device, operates by transporting small minority base charge densities <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\sim\!\! {\hbox {10}}^{16}\ {\hbox {cm}}^{-3}$</tex></formula> over nanoscale base thickness ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$&lt;$</tex></formula> 900 A) in picoseconds. The base QW acts as an optical “collector,” in addition to the usual electrical collector, that selects out “fast” recombining carriers, resulting in a short lifetime ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\sim$</tex></formula> 29 ps) and higher differential laser gains. Charge and current continuity, together with the boundary conditions imposed by both collectors of the TL lead to a new charge control model, “unpinning” of population inversion beyond lasing threshold, quasi-Fermi level discontinuity across base QW, and a new equivalent circuit model requiring an extension to Kirchhoff's law. With the TL, the HBT becomes more than just a charge control device, but also a photon storage and switching device. The TL, owing to fast recombination speed, its unique three-terminal configuration, and the complementary nature of its optical and electrical collector output signals, enables resonance-free base current and collector voltage modulations, and compact realization of electro–optical applications such as nonlinear signal mixing, frequency multiplication, negative feedback, and optoelectronic logic gates.

Heterostructures for Optoelectronics: History and Modern Trends

Semiconductor revolution of the 20th century determined not only technological, but also social development of the modern society. The precursors of modern semiconductor electronics were Oleg Losev's discoveries of “crystadine” and “light-emitting diode (LED)” nearly 100 years ago. Creation of the transistor and semiconductor laser and LED based on the homo p-n structure became the most decisive step. Semiconductor optoelectronics was born with the creation of GaAs and GaAsP lasers and “LED.” The possibility to control the type and level of conductivity and injection in p-n junctions was the seed from which semiconductor electronics developed. Heterostructures-“man-made crystals”-solved a more general problem: the necessity to control electron and photon fluxes in crystals. The development of physics and technology for semiconductor heterostructures resulted in drastic changes in our everyday life. It is hardly possible to imagine our recent life without double-heterostructure (DH) laser-based telecommunication systems, without efficient DH LEDs, heterostructure bipolar transistors, and high electron mobility transistors (HEMTs) for high-frequency applications. DH lasers were introduced in every household with CD players. Heterostructure solar cells have been widely used for space and terrestrial applications. The first proposals for heterostructures in semiconductor devices were made as early as in the 1950s, but the most important experimental results were received at the end of the 1960s when the first ideal AlGaAs heterostructures and low threshold room-temperature lasers, efficient heterostructure LEDs, and solar cells were created. Later semiconductor heterostructure became laboratories of low-dimension electron gases. Molecular-beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) technologies were the basis for the development of new structures, including superlattices, and for the industrial production of a large family of heterostructure semiconductor devices. Quantum dot (QD)-based optoelectronics as a modern trend in optoelectronics is the subject of a more detailed consideration.

The III–V Alloy p–n Diode Laser and LED Ultimate Lamp

In this paper, an account is presented of the semiconductor, because of the energy gap bipolar with electron (e) and hole (h) conductivity, becoming ingeniously with little or no technology (Bardeen and Brattain, Dec. 1947) the transistor, a triode (at first just a germanium “base” crystal and a point contact “emitter” and “collector”), a low impedance “emitter” minority carrier input (IE) into a (the) vital central “base” active region, the base supporting along with essential recombination current I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> > 0) carrier transport to a higher impedance “collector” output I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> ( I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</sub> +I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> +I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> =0, I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</sub> =α ~ 0.9), hence gain, thus revealing at last that a current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> ) can increase the electron-hole (e-h) population, and as a further consequence, yield band-to-band (k <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> =k <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</sub> ) excess carrier recombination radiation (light). The transistor established (1947) a basis for the study of the light-emitting diode (LED). The path to an “ultimate lamp,” the p-n diode laser and LED, is described from semiconductor, to energy gap, e-h bipolarity, transistor, the p-n transition, excess carriers, e-h recombination, direct gap (k <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> =k <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</sub> ) crystal, autocatalytic e-h/photon interaction, spectral narrowing, stimulated recombination (laser), need for resonator (cavity Q, how?), direct-gap (k <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> =k <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</sub> ) III-V alloy, visible spectrum III-V alloy, III-V alloy gap change (ΔE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> ), quantum-well (QW) e-h recombination, stimulated emission solving the problem of photon extraction ( → 100% quantum efficiency), the p-n diode “ultimate lamp,” return to the 1947 triode, to the transistor, and the base importance informing the realization of a QW-base transistor laser.

Simulation of deep level traps effects in quantum well transistor laser

In this paper, we present an analytical model to analyze the influence of deep level traps on the static and dynamic responses of transistor laser (TL). Our analyze is based on analytically solving the continuity equation and rate equations including the effect of the deep level trap (DLT), which incorporate the virtual states as a conversion mechanism. The results of simulation show that the main characteristics of laser such as threshold current, quantum efficiency, output power, and modulation bandwidth are affected by total density of traps in the active region.

Design and Characterization of AlGaInAs/InP Buried Heterostructure Transistor Lasers Emitting at 1.3-μm Wavelength

We discuss the wafer design and fabrication process for the 1.3-μm-wavelength AlGaInAs/InP transistor lasers, and the structural dependence of lasing and the electrical characteristics are shown. We particularly focus on the base structure, and the thickness and width dependence are numerically and experimentally analyzed. A thicker base layer resulted in lower optical confinement factor in the quantum wells (QWs), higher optical loss, and lower current gain. In addition, a wider base width caused leak current recombination outside the QWs. By modifying the structure of an n-p-n TL, it was possible to simultaneously realize room-temperature continuous-wave lasing and transistor operation.

Selective oxidization cavity confinement for low threshold vertical cavity transistor laser

Data are presented for a low threshold n-p-n vertical cavity transistor laser (VCTL) with improved cavity confinement by trench opening and selective oxidation. The oxide-confined VCTL with a 6.5 × 7.5 μm2 oxide aperture demonstrates a threshold base current of 1.6 mA and an optical power of 150 μW at IB = 3 mA operating at −80 °C due to the mismatch between the quantum well emission peak and the resonant cavity optical mode. The VCTL operation switching from spontaneous to coherent stimulated emission is clearly observed in optical output power L-VCE characteristics. The collector output IC–VCE characteristics demonstrate the VCTL can lase in transistor's forward-active mode with a collector current gain β = 0.48.

Analytical model for threshold‐base current of a transistor laser with multiple quantum wells in the base

The authors investigate in this study the effect of incorporating multiple quantum wells (QWs) in the base of a heterojunction bipolar transistor laser on its performance. The expression for the terminal current is obtained by solving continuity equation in the base relating the bulk carrier density with the two-dimensional (2D) carrier density via virtual states. The gain in the QW is obtained by considering strain, 2D density-of-states, polarisation dependent momentum matrix element, Fermi statistics and Lorentzian broadening. The authors have taken as the basis for comparison the calculated as well as the experimental threshold-base current of 21.5 mA for a 16 nm wide InGaAs QW in GaAs base placed at 59 nm away from the emitter junction. Calculated value of 7.06 mA for three 16 nm wide QWs placed at 29, 59 and 79 nms in the base indicate substantial reduction in threshold-base current. Calculations are also made for three QWs of different widths having variable barrier widths. Reduction of threshold-base current by different amounts is observed in all cases.

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.

Transient characteristics of the InGaP–GaAs–InGaAs–GaAs transistor laser

Transient characteristics of the InGaP–GaAs–InGaAs (quantum well)-GaAs transistor laser are studied. Rate equations are numerically solved to obtain the response of current density and photon density. Expression of resonance frequency \(f_{r}\) is obtained by solving the rate equations analytically. It has been found that the \(f_{r}\) increases with decreasing spontaneous carrier lifetime and with increasing value of the bias current density.

Performance Optimization of Multiple Quantum Well Transistor Laser

A comprehensive physical model that emphasizes carrier tunneling between quantum wells (QWs) in the base of transistor lasers (TLs) is developed. This model relies on a set of multilevel coupled rate equations solved by computationally efficient numerical methods for simulating both steady state and transient TL operations. Our approach also features the explicit dependence of the structure design on device parameters such as optical confinement factor and carrier density-dependent gain. It also accounts for operation behaviors such as bandwidth roll-off and critical base width not yet addressed in the literature. Simulation results show significant enhancement in optical bandwidth as well as threshold current reduction when multiple QWs are incorporated within the base region. It predicts the dominance of tunneling transport of carriers for barriers thinner than 13.5 nm in a system with 7-nm QWs. However, the optimum QW number depends on the structure design as well as TL biasing conditions. For this purpose, we define a performance parameter as a TL figure of merit that can be maximized by optimizing both the base and the cavity designs.

Room-Temperature Continuous-Wave Operation of npn-AlGaInAs Transistor Laser Emitting at 1.3-$\mu{\rm m}$ Wavelength

Room-temperature continuous-wave operation of a 1.3-μm npn-AlGaInAs/InP transistor laser is successfully achieved for the first time. A threshold current of 39 mA and an external differential quantum efficiency of 13% are obtained under common base operation, while simultaneous transistor action is achieved with a current gain β of 0.02.

The effect of ground and first excited state transitions on transistor laser relative intensity noise

We report the results of relative intensity noise (RIN) measurement on the ground and first excited state transitions of a single quantum-well (QW) transistor laser (TL). Because of higher differential gain and faster recombination lifetime on the first excited state transition, a lower laser RIN is measured as compared with ground state laser operation. The minority carrier density in the base of QWTL extracted from the laser RIN shows a carrier density of 2.6–3.5 × 1016 cm−3, a more than 40× reduction from that of a conventional diode laser.

A nonlinear gain model for multiple quantum well transistor lasers

The gain spectra of single quantum well (SQW) heterojunction bipolar transistor laser (HBTL) is calculated with the gain coefficients and transparency carrier density as a function of the device structure factors by taking into account intraband relaxation. Inter-well coupling effects in a multiple quantum well (MQW) structure are considered as a correction factor in our approach. We introduce a six-order polynomial expression for a nonlinear carrier-dependent gain of MQW-HBTL considering ground, first excited and second excited states. We show that our gain model is notably more accurate than usual logarithmic equations, particularly in a large signal regime. Using computationally efficient numerical methods with a comprehensive rate-equation-based model, we obtain good agreement with experimental results for small signal, large signal and switching analysis of the SQW and MQW structures. We discuss the influence of different structure factors on the switching behaviour as well as on the optical bandwidth of the HBTL. Specifically, turn-on times (τon) of 160 and 540 ps are obtained for SQW and 4 QW structures, while τon considerably decreases below 100 ps for 6 QWs due to competing effects between tunneling and thermionic emission followed by carrier diffusion over the barriers. Finally, τon can be minimized independently of the QW number when a barrier width of ≈7 nm is used in the HBTL structure.

Optimal quantum well width and the effect of quantum well position on the performance of transistor lasers

Transistor laser (TL) model based on InGaP/GaAs/InGaAs/GaAs is analyzed and presented. It is realized that quantum well (QW) with width of 10 nm may be formed for low base threshold current density J th. The emission wavelength is found to be 1.05 μm, and the indium (In) composition is 0.25 for optimal QW width. It is identified that J th decreases with the movement of QW towards the base-emitter (B-E) interface. Small signal optical response is calculated, and the effect of QW position is studied. The bandwidth is enhanced due to the movement of the QW towards the emitter base junction.

Base Width Variations and its Effects on Frequency Response of Double Hetero-structure Long Wavelength Transistor Laser

In this paper we investigate the effects of base width variation on performance of long wavelength transistor laser. In our structure with increasing the base width, the cut off frequency increases until 367 nm with 24.5 GHz and then abruptly fall. In 100 nm base width, we have 17.5 GHz cut off frequency, and overall ac performances become optimized, although, other parameters like optical losses and threshold current density are not optimized.