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-singal 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.

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 nearly constant current peak-to-valley ratio is demonstrated.

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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.