This paper describes the progress of AlInAs/GaInAs HBT devices and ICs. A cutoff frequency (fT) and a maximum frequency of oscillation of 130 GHz and 91 GHz, respectively, have been achieved with graded base-emitter junctions. A divide-by-four circuit clocked at 39.5 GHz, an 8/9 dual modulus divider consisting of 128 transistors clocked at 9 GHz, a broad band amplifier with 8 dB gain and 33 GHz bandwidth, and a dc-to-16-GHz Gilbert Gain Cell active mixer will be described.
A high-performance AlGaAs/GaAs HBTIC technology capable of 45 GHz fT and fmax is described. The process is mesa isolated and does not use any ion-implantation steps. This simple non-self-aligned process integrates 1.4 THz Schottky diodes, nichrome resistors, MIM capacitors and air-bridge inductors. An HBT divide-by-eight prescaler circuit clocks at 13.5 GHz. A pulser circuit using the fast Schottky diodes produced a voltage pulse having 10.35 ps rise time.
This is a review of general characteristics of Heterojunction Bipolar Transistors (HBTs) and the status of Optoelectronic Integrated Circuits (OEICs) with HBT-based electronics. We also analyze different approaches taken at the present for the monolithic integration.
AlGaAs/GaAs Narrow Base Heterojunction Bipolar Transistors (NBHBTs) with 50 angstroms thick bases exhibit maximum small signal common emitter current gains hfe of 1400 at 300 K and 3000 at 80 K. The performance of the device is attributed to the superlattice graded emitter contact and a novel planar base access fabrication process. Low temperature measurements indicate that the maximum current gain increases exponentially with decreasing temperature until is saturates around 200 K, suggesting a tunnelling limited current transport mechanism.
The advantages of using Sb containing III-V compounds in bipolar type devices are discussed with recent experimental results of two different applications of GaAsSb in Heterojunction Bipolar Transistors (HBTs). The performance of a prototype AlGaAs/GaAsSb/GaAs double HBT (DHBT) that exhibits a current gain of five and a maximum collector current density of 5 X 104 A/cm2 and a pnp AlGaAs/GaAs HBT with a superlattice GaAsSb emitter ohmic contact, with specific contact resistivity of 5 +/- 1 X 10-7 (Omega) -cm2 across the sample, are examined.
Advanced high electron mobility transistors (HEMTs) and MMICs, currently under development at GE for a variety of power and low noise applications at frequencies ranging from 1 to 100 GHz, is reviewed, and future trends are projected.
The frequency dependencies of minimum noise figure (Fmin) and associated gain (Ga) of extrinsic MODFETs have been fit with the resistor temperature noise model for intrinsic FETs of Pospieszalski. The noise model for extrinsic MODFETs has two fitting parameters; an effective fmax and an effective output resistor temperature (Td) which are extracted directly from the measured Fmin and Ga. A comparison of noise results in more than 50 publications shows that the majority of MODFETs can be modelled with a small range of effective Td values between 300 and 700 K. AlInAs/GaInAs/InP MODFETs exhibit significantly lower Fmins and Gas than conventional AlGaAs/GaAs and AlGaAs/InGaAs pseudomorphic MODFETs of the same gate length. The reason is InP-based MODFETs have a much higher average fmax(DOT)Lg at low noise bias. The noise model implies that in addition to a high fT and low Rin, a lower Gds also reduces Fmin. Also, it suggests that the Fukui fitting factor (Kf) is proportional to the inverse square root of the voltage gain. Recent experimental results support this suggestion. The noise model and the analyses of published results show that a higher fmax at low noise bias is a key factor for a lower Fmin and a higher Ga.
A discrete peeled high electron mobility transistor (HEMT) device was integrated into a 10 GHz amplifier. The discrete HEMT device interconnects were made using photo patterned metal, stepping from the 10 mil alumina host substrate onto the 1.3 micrometers thick peeled GaAs HEMT layer, eliminating the need for bond wires and creating a fully integrated circuit. Testing of device indicate that the peeled device is not degraded by the peel off step but rather there is an improvement in the quantum well carrier confinement. Circuit testing resulted in a maximum gain of 8.5 dB and a return loss minimum of -12 dB.
We have generated picosecond optical pulses with very pure spectral characteristics using semiconductor lasers with monolithic cavities. For repetition rates less than 10 GHz, gain- switching of DFB lasers with quantum well loss-gratings is used. Monolithic colliding pulse mode-locked semiconductor lasers are used to generate short pulses with repetition rate up to 350 GHz.
The maximum possible intrinsic modulation in semiconductor lasers is conventionally written in terms of the K factor. Although this is often sufficient in bulk lasers, it is usually not true in quantum well lasers where carrier transport can significantly affect the high speed properties. Here we present analytical expressions, which include the effects of carrier transport, for the modulation response and the relative intensity noise in quantum well lasers. We show that in the presence of significant transport effects, the K factor is not an accurate measure of the maximum possible intrinsic modulation bandwidth.
The low frequency response and damping behavior of four quantum well (4QW) graded-index separate confinement heterostructure (GRINSCH) and SCH strained-layer lasers are compared. The SCH laser is shown to be better in both respects due to a shorter carrier capture time into the quantum wells. A record 3-dB bandwidth of 28 GHz is reported for a 150 micrometers cavity length 4QW strained-layer SCH laser. The change in the differential gain, non-linear gain coefficient, and damping rate are studied as a function of the quantum well thickness and barrier height. It is found that decreasing the well thickness does not change the non-linear gain coefficient nor the differential gain appreciably in relatively deep wells. Shallower quantum wells, however, are observed to have lower differential gain and a higher damping rate.
The maximum 3 dB modulation bandwidth of a semiconductor laser is determined, if not by RC or power limits, by damping that arises from photon-dependent suppression of the optical gain. In bulk lasers this damping limit is found, both experimentally and analytically, to be relatively constant at 25 - 45 GHz, independent of device design. In contrast, the damping limit is found to vary widely for quantum well lasers. In this paper we will describe experimental results showing the structure dependence of the damping, and we will present evidence for a new model explaining the structure dependence as a result of well-barrier hole burning. This hole burning arises from a buildup of carriers in the barrier layers due to the nonzero carrier capture times of the wells, causing a spatial hole to be burned perpendicular to the active region. This hole can behave like a photon dependent gain suppression, leading to a larger nonlinear gain parameters and a lower effective differential gain. We also suggest ways to optimize quantum well laser structures for maximum modulation bandwidth.
A reflectometer technique using scalar optoelectronic measurements has been proposed to correct source mismatch errors. The merits of different detector configurations and the measurement system requirements have been discussed. A GaInAs photodiode has been measured to 40 GHz using a DFB laser heterodyne system. Results corrected for source mismatch using reflection coefficient measurements have been compared with results measured by the reflectometer technique. Agreement between the two corrected optoelectronic responses is better than 0.2 dB.
System demonstrations employing soliton transmission and/or optical time division multiplexing have emphasized the need for stable and reliable pulse sources with repetition rates in the 1 GHz to 10 GHz range. For these applications, we have fabricated several photonic integrated laser devices that through gain-switching or mode-locking generate optical pulses with durations between 20 ps and 50 ps. In this talk, we will discuss gain-switched DBR laser integrated with high-power optical amplifiers or electro-absorption modulators and laser devices with long low-loss passive waveguides for active mode-locking.
We discuss the properties and performance of state-of-the-art barrier enhanced InGaAs metal- semiconductor-metal (MSM) photodetectors, for use at 1.3 micrometers and 1.55 micrometers wavelengths. Different device characteristics, such as response, capacitance, and speed, are considered. Integration with transistors of form monolithic receivers and with semiconductor waveguides to form pre-detection optical processing circuits, is also discussed.
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.
We have demonstrated the fabrication of two structures achieved by the thin ifim transfer technique: back4lluminated InAlAsfInGaAs metal. semiconducthr-metal (MSM) detectors with buried interdigitated fingers on GaAs substrates; and long wavelength InGaAsP lasers on GaAs or Si substrates. For optoelectromc system applications, one often considers the use of a single material system for both the optical and electronic components on the chip, because it is not complicated by lattice mismatch. Compared to epitaxial growth of latticemismatched material systems, such as GaAs on Si, the thin ifim transfer technique does not result in a substantial number of misfit dislocations which can adversely affect device performance. The results we obtained demonstrate the feasibility of the thin film transfer process and point to the potential integration of OEICs and other components fabricated from a variety of materials on a common host substrate.
GaSh-based meta1semiconductor-meta1 (MSM) and pi-n photodetectors grown by molecular beam epitaxy have been demonstrated for the first time. These novel devices can offer higher bandwidths and lower excess noise because of the superior hole transport properties of GaSb and the enhanced hole ionization rate of A1GaSb alloys. MSM photodetectors employing GaSb active region and AlGaSb barrier enhancing abrupt region are grown on InP substrates, while p4n photodiodes are grown on GaSb substrates. These MSM detectors exhibit photoresponse in the range of 0.2-0.65 AJW and a 3 dB bandwidth exceeding 1 GHz at 300 K and 10 GHz at 77 K. The dark currents of 106 A at 300 K and 1010 A at 77 K are measured for 25 x 25 devices. The p-i-n photodiodes have breakdown voltages as high as 20 V. The leakage currents of these devices are 60 i.i.A at half the breakdown voltage and 10 pA after nitrogen plasma passivation for 40 x 40 devices. To the best of our knowledge, these are the best results obtained from the structures grown by MBE.