P.J. Tasker

Control of differential gain, nonlinear gain and damping factor for high-speed application of GaAs-based MQW lasers

Utilizing small-signal direct modulation and relative intensity noise measurements, the authors investigate changes in the modulation response, the differential gain delta g/ delta n, the nonlinear gain coefficient in , and the damping factor K, which result from three structural modifications to GaAs-based multiple quantum well lasers: the addition of strain in the quantum wells; and increase in the number of quantum wells; and the addition of p-doping in the quantum wells. These modifications are assessed in terms of their potential for reducing the drive current required to achieve a given modulation bandwidth, for increasing the maximum intrinsic modulation bandwidth of the laser, and for improving the prospects for monolithic layer/transistor integration. It has been possible to simultaneously increase delta g/ delta n and decrease K, yielding very efficient high-speed modulation (20 GHz at a DC bias current of 50 mA) and the first semiconductor lasers to achieve a direct modulation bandwidth of 30 GHz under DC bias. >

Impedance characteristics of quantum-well lasers

We derive theoretical expressions for the impedance of quantum-well lasers below and above threshold based on a simple rate equation model. These electrical laser characteristics are shown to be dominated by purely electrical parameters related to carrier capture/transport and carrier re-emission. The results of on-wafer measurements of the impedance of high-speed In/sub 0.35/Ga/sub 0.65/As/GaAs multiple-quantum-well lasers are shown to be in good agreement with this simple model, allowing us to extract the effective carrier escape time and the effective carrier lifetime, and to estimate the effective carrier capture/transport time.<<ETX>>

Transistor noise parameter extraction using a 50 Omega measurement system

A 50- Omega noise-figure measurement system has been integrated into a fully automated S-parameter measurement system, allowing fast determination of transistor noise parameters as well as S-parameters as a function of both frequency and bias. This functionality from such a simple measurement system is achieved using a novel analysis technique, based on the noise temperature model (see M.W. Popieszalski, 1989), that allows, after S-parameter measurements and analysis, the direct extraction of all four transistor noise parameters from a single noise-figure measurement. The value of the unknown temperature T/sub d/ and the physically relevant small-signal model circuit element values determined provide the CAD (computer-aided design) database necessary to model both the scaling behavior of the transistor S-parameters and noise parameters and their extrapolation to millimeter-wave frequencies.<<ETX>>

New MODFET small signal circuit model required for millimeter-wave MMIC design: extraction and validation to 120 GHz

A new MODFET circuit model required for millimeter-wave MMIC design has been developed, since it was found conventional MODFET circuit topology normally used was not able to accurately simulate measurement data above 75 GHz. This new model accounts for distributed effects in the transistor layout and includes a modified intrinsic transistor circuit topology. This circuit model has been experimentally validated by on-wafer S-parameter measurements performed to 120 GHz. This was made possible by the development of two advanced millimeter-wave on-wafer S-parameter measurement systems.<<ETX>>

Attenuation of millimeterwave coplanar lines on gallium arsenide and indium phosphide over the range 1-60 GHz

Extensive attenuation data of coplanar lines on semi-insulating GaAs and InP are presented over the frequency range 1-60 GHz. On-wafer measurements were used to obtain the S-parameters. A ground-to-ground spacing of 30, 60, and 120 mu m, typical of that used in todays microwave and millimeter-wave integrated circuit applications, was investigated. The center line width (impedance) and the evaporated gold metal thickness were varied. For the frequency range investigated (metal thickness less than 2-3 times the skin depth), the attenuation was found to be inversely proportional to the metal thickness.<<ETX>>

p-Dopant incorporation and influence on gain and damping behaviour in high-speed GaAs-based strained MQW lasers

Abstract We investigate p-dopant incorporation and the influence of p-doping on the gain and damping behaviour in GaAs-based strained multiple quantum well lasers. By adding 5 × 10 18 –2 × 10 19 cm –3 beryllium doping to the active region of In 0.35 Ga 0.65 As/GaAs strained multiple quantum well lasers (4 QWs), we are able to demonstrate both very efficient high-speed modulation (20 GHz at a DC bias current of 50 mA) and the first semiconductor lasers to achieve a direct modulation bandwidth of 30 GHz under DC bias (heat-sink temperature = 25°).

High performance narrow and wide bandwidth amplifiers in CPW-technology up to W-band

Several millimeter-wave MMICs were fabricated successfully using 0.16 /spl mu/m pseudomorphic MODFET technology. A five-stage distributed amplifier has 9.3 dB gain over the frequency range 5 GHz to 80 GHz and a noise figure less than 4.3 dB up to 60 GHz. A narrowband three-stage low noise amplifier delivers more than 21 dB gain between 70 and 80 GHz. For the first time Cascode transistors in CPW-technology were used for a distributed amplifier achieving a gain bandwidth product of 744 GHz*dB.<<ETX>>

16-GHz GaAs/AlGaAs multiple-quantum-well laser with vertically compact waveguide structure

A GaAs/AlxGa1-xAs multiple quantum well laser with a 3 dB electrical modulation bandwidth of 16 GHz has been developed. Optimized design of the waveguide, including implementation of high average Al mole fraction (xeff equals 0.8) GaAs/AlAs binary short-period superlattice cladding layers, together with a coplanar electrode geometry, has resulted in a vertically compact laser structure suitable for integration.

Impedance, modulation response, and equivalent circuit of ultra-high-speed InGaAs/GaAs MQW lasers

We present the first direct on-wafer measurements of the electrical impedance of p-doped In/sub 0.35/Ga/sub 0.65/As/GaAs MQW lasers, and use the results to derive an equivalent circuit model for frequencies up to 50 GHz. In order to explain the impedance characteristics, the effects of carrier capture into the QWs as well as the space-charge capacitance of the diode junction must be taken into account. Utilizing this equivalent circuit in conjunction with intrinsic laser parameters derived from RIN measurements, the electrical modulation response curves can be fitted accurately up to 40 GHz.<<ETX>>

Carrier transport effects in undoped In/sub 0.35/Ga/sub 0.65/As/GaAs MQW lasers determined from high-frequency impedance measurements

The authors have recently reported the use of high-frequency impedance measurements to obtain information about the carrier capture/re-emission processes in ultra-high-speed (30 GHz modulation bandwidth) p-doped In/sub 0.35/Ga/sub 0.65/As/GaAs MQW lasers. By using this approach the authors demonstrated: i) that the interplay between carrier capture and re-emission is not strongly affecting the high-speed modulation dynamics of these devices; and ii) that a bias dependent RC like roll-off with an associated time constant /spl tau//sub 0/, is still limiting the modulation bandwidth. In the paper the authors apply the impedance method to lasers with the same epilayer structure as those reported previously, but with nominally undoped active layers. In addition to the time constant /spl tau//sub 0/ they were able to extract the carrier re-emission time out of the QWs, /spl tau//sub esc/, and the effective carrier lifetime in the QWs, /spl tau//sub eff/.