RF performance and modeling of Si/SiGe resonant interband tunneling diodes

The RF performance of two different Si-based resonant interband tunneling diodes (RITD) grown by low-temperature molecular beam epitaxy (LT-MBE) were studied. An RITD with an active region of B δ-doping plane/2 nm i-Si_0.5Ge_0.5/1 nm i-Si/P δ-doping plane yielded a peak-to-valley current ratio (PVCR) of 1.14, resistive cutoff frequency (f_r0) of 5.6 GHz, and a speed index of 23.3 mV/ps after rapid thermal annealing at 650°C for 1 min. To the authors´ knowledge, these are the highest reported values for any epitaxially grown Si-based tunnel diode. Another RITD design with an active region of 1 nm p+ Si_0.6Ge_0.4/B δ-doping plane/4-nm iSi_0.6Ge_0.4/2 nm i-Si/P δ-doping plane and annealed at 825°C for 1 min had a PVCR of 2.9, an f_r0 of 0.4 GHz, and a speed index of 0.2 mV/ps. A small signal model was established to fit the measured S₁₁ data for both device designs. Approaches to increase f_r0 are suggested based on the comparison between these two diodes. The two devices exhibit substantially different junction capacitance/bias relationships, which may suggest the confined states in the δ-doped quantum well are preserved after annealing at lower temperatures but are reduced at higher temperature annealing. A comprehensive dc/RF semi-physical model was developed and implemented in Agilent advanced design system (ADS) software. Instabilities in the negative differential resistance (NDR) region during dc measurements were then simulated.