Richard Chan

Laser operation of a heterojunction bipolar light-emitting transistor

Data are presented demonstrating the laser operation (quasicontinuous, ∼200K) of an InGaP–GaAs–InGaAs heterojunction bipolar light-emitting transistor with AlGaAs confining layers and an InGaAs recombination quantum well incorporated in the p-type base region. Besides the usual spectral narrowing and mode development occurring at laser threshold, the transistor current gain β=ΔIc∕ΔIb in common emitter operation decreases sharply at laser threshold (6.5→2.5,β>1).

Room temperature continuous wave operation of a heterojunction bipolar transistor laser

Continuous wave laser operation at 25°C, with simultaneous electrical gain, of an InGaP–GaAs heterojunction bipolar transistor laser, with AlGaAs optical confining layers and an InGaAs recombination quantum well incorporated into the p-type base region, is demonstrated. At laser threshold (IB=40mA, VCB=0, 25°C), the transistor current gain β=ΔIC∕ΔIB in common-emitter operation changes abruptly (2.3→1.2,β>1), with laser modes developing at wavelength λ∼1006nm. Direct three-port modulation of the transistor laser at 3GHz is demonstrated for a device with a 2.2μm emitter width and a 850μm length between cleaved Fabry–Perot facets (which is the performance of an exploratory device and not near the limits).

Quantum-well-base heterojunction bipolar light-emitting transistor

This letter reports the enhanced radiative recombination realized by incorporating InGaAs quantum wells in the base layer of light-emitting InGaP/GaAs heterojunction bipolar transistors (LETs) operating in the common-emitter configuration. Two 50 A In1−xGaxAs (x=85%) quantum wells (QWs) acting, in effect, as electron capture centers (“traps”) are imbedded in the 300 A GaAs base layer, thus improving (as a “collector” and recombination center) the light emission intensity compared to a similar LET structure without QWs in the base. Gigahertz operation of the QW LET with simultaneously amplified electrical output and an optical output with signal modulation is demonstrated.

Carrier lifetime and modulation bandwidth of a quantum well AlGaAs∕InGaP∕GaAs∕InGaAs transistor laser

A quantum well (160A) 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 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).

Collector current map of gain and stimulated recombination on the base quantum well transitions of a transistor laser

Data are presented showing significant structure in the collector I-V characteristics of a transistor laser, a decrease (“compression”) in the common-emitter gain (β≡ΔIC∕ΔIB), that can be mapped in some detail and related to quantum well (QW) carrier recombination. The change in gain (β) and laser wavelength corresponding to stimulated recombination (stimulated emission) on QW transitions, which is compared with operation in spontaneous recombination (cavity Q spoiled), is used with conventional transistor charge analysis to reveal the dynamic properties of the transistor laser.

Signal mixing in a multiple input transistor laser near threshold

A single-emitter multiple-input transistor laser has been realized and demonstrated in signal mixing, yielding in the stimulated-recombination region near laser threshold frequency conversion with simultaneously an electrical and optical output signal. In the unique nonlinear region of compression of the transistor I-V characteristics (β≡ΔIC∕ΔIB, βspon>βstim), input signals f1=2GHz and f2=2.1GHz are converted into mf1±nf2 ranging from 0.1to8.4GHz. Stimulated emission (enhanced recombination) changes the transistor into a special form of nonlinear element, a special form of electronic processor or “switch.”

Microwave operation and modulation of a transistor laser

The microwave operation and modulation (3GHz) of an InGaP∕GaAs heterojunction bipolar transistor (HBT) laser is reported. The HBT layer structure is in the form of an optical waveguide (with cleaved ends) that also includes an InGaAs recombination quantum well in the p-type base region to improve the recombination radiation properties. The shift in HBT laser operation from spontaneous to stimulated emission is manifest as a distinct change in the HBT current–voltage characteristics, specifically a decrease in the common-emitter current gain (βdc=IC∕IB) and the occurrence of even a more striking peak in the small signal (ac) gain βac=ΔIC∕ΔIB.

Collector breakdown in the heterojunction bipolar transistor laser

Data are presented on a quantum-well (QW)-based InGaP∕GaAs∕InGaAs (QW) heterojunction bipolar transistor laser modified with external (increased) mirror reflection yielding lower threshold current (IB=23→19mA) and higher collector breakdown voltage (⩾2.5V). Increased breakdown at lower currents is observed on the collector I-V characteristics, at constant base current IB, as a slope change, a corner, and a narrow-line to broadband spectral shift from stimulated (high coherent optical field) to spontaneous (lower incoherent field) operation, a consequence of quenching or reducing photon-assisted tunneling (Franz-Keldysh effect) under the constraint IE+IB+IC=0 as α→1(α≡ΔIC∕ΔIE).

High-speed (/spl ges/1 GHz) electrical and optical adding, mixing, and processing of square-wave signals with a transistor laser

This letter reports the common-emitter operation (gain beta=DeltaI_C/DeltaI_B>1, 20degC, I_B=36 mA, lambda=970 nm) of a dual-input transistor laser, arranged with a separate base contact on either side of a single emitter, that adds, mixes, and processes high-speed square-wave electrical inputs and delivers separate electrical and optical outputs. Applying a square-wave electrical input X₁(t) to one base contact and X₂(t) at a second base input, we obtain, with the pulsewidth modulated because of mixing, an electrical output proportional to betatimes[X₁(t)+X₂(t)] and a laser output tracking the electrical output (hnutimesf[X₁(t)+X₂(t)]) and exceeding it in bandwidth (pulse sharpness)

Type-II GaAsSb/InP heterojunction bipolar light-emitting transistor

We report radiative recombination in the base layer of Type-II InP/GaAsSb/InP double heterojunction bipolar light-emitting transistors (HBLET) operating in the common-emitter configuration. The typical current gain, β, for a 120×120 μm2 emitter area of the HBLET is 38. The optical emission wavelength from a 30 nm GaAs0.51Sb0.49 base is centered at λpeak=1600 nm. Three-port operation of the Type-II HBLET with simultaneously an amplified electrical output and an optical output with signal modulation is demonstrated at 10 kHz.