A. Fathimulla

Frequency-Selective Predistortion Linearization of RF Power Amplifiers

This paper presents a frequency-selective RF vector predistortion linearization system for RF multicarrier power amplifiers (PAs) affected by strong differential memory effects. Differential memory effects can be revealed in two-tone experiment by the divergence for increasing tone-spacing of the vector Volterra coefficients associated with the lower and upper intermodulations tones. Using large-signal vector measurement with a large-signal network analyzer, a class-AB LDMOS RF PA is demonstrated to exhibit a strong differential memory effect for modulation bandwidth above 0.3 MHz. New frequency-selective RF and baseband predistortion linearization algorithms are proposed to separately address the linearization requirements of the interband and inband intermodulation products of both the lower and upper sidebands. Theoretical verification of the algorithms are demonstrated with Matlab simulations using a Volterra/Wiener PA model with memory effects. The baseband linearization algorithm is next implemented in a field-programmable gate array and experimentally investigated for the linearization of the class-AB LDMOS PA for two carrier wideband code-division multiple-access signals. The ability of the algorithm to selectively linearize the two interband and four inband intermodulation products is demonstrated. Adjacent channel leakage ratio of up to 45 dBc for inband and interband are demonstrated experimentally at twice the typical fractional bandwidth.

Kink effect in submicrometer-gate MBE-grown InAlAs/InGaAs/InAlAs heterojunction MESFETs

The authors report the influence of the kink effect on the DC and microwave performance of i-InAlAs heterojunction doped-channel MESFETs lattice matched to an InP substrate with submicrometer gates. Kink effects were observed at room temperature as well as at 77 K in the DC measurement. The kinks seem to be related to deep-level electron trapping, and are not present at microwave frequencies. Measured results are presented showing that the existence of kinks at low operating frequencies does not seem to degrade the microwave performance of the devices.<<ETX>>

Three‐dimensional integration of resonant tunneling structures for signal processing and three‐state logic

We have developed structures with two well‐defined negative differential resistance (NDR) regions by sequentially growing two resonant tunneling devices separated by an n+ connecting layer. Devices fabricated from these structures exhibited three stable operating points for multilevel logic circuits and were used in circuits which multiplied the input signal frequency by 3 or 5. This approach can be extended to obtain more than two NDR regions by vertical integration of additional resonant tunneling structures.

High-performance InAlAs/InGaAs HEMTs and MESFETs

The fabrication and microwave performance of heterostructure InAlAs/InGaAs HEMTs (high-electron-mobility transistors) and MESFETs are described. Maximum stable gains of 14.3 dB for a HEMT and 12 dB for a MESFET at 26.5 GHz have been achieved. These are believed to be record gains for FETs having gates as long as 0.7 mu m.<<ETX>>

Interface roughness scattering in AlAs/InGaAs resonant tunneling diodes with an InAs subwell

We present simulation results on the current‐voltage (I‐V) characteristics of an InP‐based AlAs/InGaAs resonant tunneling diode (RTD) with InAs subwell. Space‐charge limited transport is accounted for using a self‐consistent electrostatic potential calculated using the Hartree approximation. Three‐dimensional scattering is simulated using the recently developed multiple sequential scattering theory. Interface roughness scattering is found to be dominant over polar phonon scattering in the devices studied. Of particular interest is interface‐roughness (IR) scattering at the InGaAs/AlAs and InGaAs/InAs interfaces and its impact on the valley current. The existence of a critical terrace size that maximizes IR scattering is identified through simulation. The origin of the asymmetry commonly measured in the RTD I‐V characteristic is discussed with respect to asymmetries in interface scattering. The use of the InAs subwell and associated interface roughness scattering to tune the peak current while keeping a ne...

Halogen lamp rapid thermal annealing of Si- and Be-implanted In0.53Ga0.47As

Halogen lamp rapid thermal annealing was used to activate 100 keV Si and 50 keV Be implants in In0.53Ga0.47As for doses ranging between 5 × 1012−4 × 1014 cm−2. Anneals were performed at different temperatures and time durations. Close to one hundred percent activation was obtained for the 4.1 × 1013 cm−2 Si-implant, using an 850° C/5 s anneal. Si in-diffusion was not observed for the rapid thermal annealing temperatures and times used in this study. For the 5 × 1013 cm−2 Be-implant, a maximum activation of 56% was measured. Be-implant depth profiles matched closely with gaussian profiles predicted by LSS theory for the 800° C/5 s anneals. Peak carrier concentrations of 1.7 × 1019 and 4 × 1018 cm−3 were achieved for the 4 × 1014 cm−2 Si and Be implants, respectively. For comparison, furnace anneals were also performed for all doses.

OMVPE growth of AlInAs and device quality AlInAs-based heterostructures

Abstract High-quality AlInAs exhibiting excellent photoluminescence and having residual electron concentrations as low as 7×10 15 cm −3 with electron mobilities as high as 1900 cm 2 /V·s has been grown by OMVPE. AlInAs/InP heterostructures are shown to be type II heterojunctions with electron mobilities as high as 4500 cm 2 /V·s at 300 K. This material was used for the fabrication of high-gain heterostructure MESFETs and heterostructure insulated-gate FETs (HIGFETs). AlInAs/InP MESFETs have DC transconductances as high as 220 mS/mm and microwave gains as high as 11.5 dB at 10 GHz with an max of 42 GHz. AlInAs/InP/GaInAs HIGFETs, however, show high transconductances up to 470 mS/mm at 300 K and 530 mS/mm at 77 K. These are some of the highest performance FETs fabricated on OMVPE-grown material.

Second subband population in δ‐doped Al0.48In0.52As/Ga0.47In0.53As heterostructures

We have observed the population of the second two‐dimensional electron subband in δ‐doped Al0.48In0.52As/Ga0.47In0.53As heterostructures by Shubnikov–de Haas measurements. After illuminating the samples at low temperature, the electron density increases from 17.3 to 18.2×1011 cm−2 for the first subband and from 3.6 to 4.1×1011 cm−2 for the second subband. The population of the second subband begins when the first subband is filled at a density of 10.3×1011 cm−2. The effective mass of the second subband is equal to (0.045±0.003)m0, indicating significant band nonparabolicity in the Ga0.47In0.53As well.

Monolithic integration of InGaAs/InAlAs MODFETs and RTDs on InP-bonded-to Si substrate

The authors report the monolithic integration of InGaAs/InAlAs MODFETs and RTDs MBE grown using selective epitaxy on InP which has been bonded to a silicon substrate. The study demonstrates the feasibility of monolithically integrating III-V devices having different heterostructures with silicon devices.<<ETX>>

Multiple subband population in delta-doped AlAsSb/InGaAs heterostructures

We have measured the Shubnikov–de Haas (SdH) effect in δ-doped AlAs0.56Sb0.44/In0.53Ga0.47As heterostructures and observed a population of the second subband. Using the persistent photoconductivity effect we increased the electron density from 26.73 to 28.20×1011 cm−2 in the first subband and 6.61 to 7.20×1011 cm−2 in the second. The onset of the second subband population occurs when the first subband is filled to a density of 11.56×1011 cm−2. From the nonparabolic band approximation we calculated the effective masses in both subbands before illumination. The effective mass for the second subband was evaluated using the temperature dependence of the SdH amplitude. Its value agrees well with the values obtained from the k⋅p approximation and infrared cyclotron resonance measurements.