A fully integrated 6-GHz phase-locked-loop (PLL) fabricated using AlGaAs/GaAs heterojunction bipolar transistors (HBTs) is described. The PLL is intended for use in multigigabit-per-second clock recovery circuits for fiber-optic communication systems. The PLL circuit consists of a frequency quadrupling ring voltage-controlled oscillator (VCO), a balanced phase detector, and a lag-lead loop filter. The closed-loop bandwidth is approximately 150 MHz. The tracking range was measured to be greater than 750 MHz at zero steady-state phase error. The nonaided acquisition range is approximately 300 MHz. This circuit is the first monolithic HBT PLL and is the fastest yet reported using a digital output VCO. The minimum emitter area was 3 mu m*10 mu m with f/sub t/=22 GHz and f/sub max/=30 GHz for a bias current of 2 mA. The speed of the PLL can be doubled by using 1- mu m*10- mu m emitters in next-generation circuits. The chip occupies a die area of 2-mm*3-mm and dissipates 800 mW with a supply voltage of -8 V. >

A 6-GHz integrated phase-locked loop using AlGaAs/GaAs heterojunction bipolar transistors

The contributions of nonlocal mechanisms to nonlinear transport in semiconductors, with special emphasis on hot‐electron emission at heterojunctions and its variations which are now commonly termed real‐space transfer effects, are reviewed. The goal is to equitably account for and bring together the body of literature that has developed, often independently, in the U.S. and the former Soviet Union as well as in Europe and Japan.

Nonlocal and nonlinear transport in semiconductors: Real-space transfer effects

A monolithic integrated driver circuit developed for laser modulation in a 10 Gb/s optical-fiber link is presented. The IC was fabricated in a self-aligned double-polysilicon Si-bipolar production technology with f/sub T//spl ap/25 GHz. The circuit can be operated up to 14 Gb/s with a maximum output voltage swing as high as 3.6 V at 50 /spl Omega/ load (corresponding to an internal current swing of 108 mA), which allows the circuit to drive external modulators. In addition, the circuit can be used for direct laser modulation at 10 Gb/s, since the output current swing can easily be controlled over a wide range (e.g., from 15 mA to 60 mA). Problems in the design of such driver circuits as well as their solutions are discussed in detail. >

A versatile Si-bipolar driver circuit with high output voltage swing for external and direct laser modulation in 10 Gb/s optical-fiber links

Carbon‐doped GaAs/AlGaAs heterojunction bipolar transistors (HBTs) typically exhibit severe leakage at the base‐emitter interface which limits their utility for low‐current applications. Furthermore, the device breakdown voltage, and hence power handling capability, is limited due to the band gap of the GaAs collector material. In this letter we will demonstrate for the first time that both of these limitations can be overcome through the use of InGaP. Since InGaP is not readily doped with carbon, it does not suffer from compensation due to carryover of carbon from the GaAs base. Hence, the ideality factor of the base‐emitter junction improves from 1.3 to 1.09 when the conventional n‐AlGaAs emitter layer is replaced with n‐InGaP. Moreover, InGaP eliminates the crossover of the base and collector currents typically observed in heavily carbon doped GaAs HBTs. This results in the maintenance of gain even at very low collector currents. As a collector material, we have found that InGaP produces significantly higher breakdown voltage than GaAs (19 V vs 12 V) of the same thickness and doping, due to its larger band gap. As in the emitter, InGaP collectors exhibit excellent ideality factors of ∼1.05.

Improved performance of carbon-doped GaAs base heterojunction bipolar transistors through the use of InGaP

Advances in MOVPE, MBE, and CBE

The very low parasitic resistance n-p-n GaAs/AlGaAs heterojunction bipolar transistors (HBT) grown by metal organic molecular beam epitaxy (MOMBE) using all gaseous source dopants are reported. The carbon and tin dopants were introduced through the uses of trimethygallium (TMGa) and tetraethyltin (TESn). To achieve the low parasitics, the graded InGaAs emitter cap layer was doped with tin to 5*10/sup 19/ cm/sup -3/ and the doping level in the subcollector was 3*10/sup 18/ cm/sup -3/. The emitter and collector sheet resistances were 25 Omega / Square Operator and 10 Omega / Square Operator , respectively. The 800 AA thick base layer was carbon doped to a level of 7*10/sup 19/ cm/sup -3/. The base contact resistance and sheet resistance were 0.1 Omega mm and 180 Omega / Square Operator , respectively. With a thin AlGaAs surface passivation layer for the emitter-base junction, the common emitter DC current gain was maintained up to 25, even for 2*5 mu m/sup 2/ emitter size devices. The unity short circuit current gain cutoff frequency f/sub T/, and maximum oscillation frequency f/sub max/, were 48 and 63 GHz, respectively.

Selfaligned AlGaAs/GaAs HBT grown by MOMBE

High performance, selfaligned processed npn and pnp AlGaAs/GaAs HBTs grown by MOMBE are reported. Tin and carbon were used as n- and p-type dopants, respectively. Cutoff frequency and maximum frequency of oscillation of 53 and 128 GHz, respectively, were obtained for npn transistors (2×5 μm2 emitter) and values of 30 and 12 GHz, respectively, were measured for pnp transistors (2×4 μm2 emitter).

Carbon and tin doped npn and pnp AlGaAs/GaAs HBTs grown by MOMBE

A 10 Gbit/s driver IC for lasers or lightwave modulators has been implemented using carbon-doped base AlGaAs/GaAs HBTs. The integrated circuit is intended for applications involving either direct or external modulation of laser sources. The circuit is capable of driving 60 mA into a 50Ω load with rise/fall times of 40 ps and generates a differential output voltage of 6 V peak to peak at 10 Gbit/s. Modifying the design slightly, a 9 V peak to peak differential output was achieved at 5 Gbit/s by switching 90 mA into a 50Ω load.

10 Gbit/s AlGaAs/GaAs HBT driver IC for lasers or lightwave modulators

The realization of collector-up light-emitting complementary charge injection transistors is reported. The devices have been implemented in molecular-beam-epitaxy-grown n-InGaAs/ InAlAs/p-InGaAs and n-InGaAs/InP/p-InGaAs heterostructures using a self-aligned process for the collector stripe definition. Electrons, injected over the wide-gap heterostructure barrier (InAlAs or InP) by the real-space transfer (RST) process, luminesce in the low-doped p-type InGaAs active layer. An essential feature of present devices, besides their self-aligned collector-up configuration, is a relatively heavy doping of the n-type emitter channel, with the sheet dopant concentration of 4X 1012 cmn2. This ensures a higher uniformity of the electric field in the channel and provides a relief from RST instabilities at a high level of collector current (linear density - 10 A/cm). Devices with InAlAs and InP barriers show rather different optical characteristics, mainly due to the different band lineups hEc/AE, in InGaAs/InAlAs and InGaAs/InP heterostructures, leading to different ratios between the RST current and the parasitic leakage of holes from the collector into the channel. At high RST current densities, the effective carrier temperature T, in the active collector layer, determined from the high-energy tails of the luminescence spectra, is strongly enhanced compared to the lattice temperature. This decreases the device radiative efficiency and leads to a thermionic emission of carriers out of the active layer.

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P.R. Smith

Papers

Selfaligned AlGaAs/GaAs HBT grown by MOMBE

Carbon and tin doped npn and pnp AlGaAs/GaAs HBTs grown by MOMBE

10 Gbit/s AlGaAs/GaAs HBT driver IC for lasers or lightwave modulators

Collector‐up light‐emitting charge injection transistors in n‐InGaAs/InAlAs/p‐InGaAs and n‐InGaAs/InP/p‐InGaAs heterostructures

Growth of GaAs/AlGaAs HBTs by MOMBE (CBE)