Analysis of heterojunction interband tunneling diodes for MMICs

Heterostructure interband tunneling diodes (HITDs) show great potential for power generation at high frequencies. Voltage controlled oscillators (VCOs) that utilize the negative differential resistance (NDR) region of the HITFET have been demonstrated and exhibit a wider tuning range than conventional FET-based VCOs. Additionally, the center frequency can be tuned by either drain or gate bias. MMIC VCOs that incorporate HITFETs require fewer passive components when compared to conventional VCO designs. A voltage controlled oscillator (VCO) consisting of an InAlAs/InGaAs interband tunneling diode connected onto the source of a heterojunction InGaAs channel FET has been demonstrated. Precise control of the center frequency (X-band) and the tuning range (~20 MHz) were achieved by varying the drain and gate voltages (~1 V) of the HITFET. Since repeatability of the HITD equivalent circuit is crucial for accurate circuit design and circuit operation, a discussion of the growth optimization and material parameters of the diodes is presented. Secondary ion mass spectrometry (SIMS), transmission electron microscopy (TEM) and electrolytic capacitance voltage (ECV) profiling are used to study the effect of dopant compensation and dopant diffusion on the I-V characteristics and the peak-to-valley current ratios (PVCRs) of the HITDs. The data shows an exponential dependence of the PVCR on oxygen background concentration in the sample. It also shows that the presence of doping impurities in the well region (which is determined using SIMS analysis) produces a dramatic degradation of the PVCR and peak current density