Design of Material Structures for Heterostructure Barrier Varactors

Paper in proceeding, 2001

The Heterostructure Barrier Varactor (HBV), first proposed by Kollberg et al. [1], has a symmetric C-V and an anti-symmetric I-V characteristic. Therefore it will only produce odd harmonics of the input frequency when used in mm- and submm-wave frequency multipliers, which greatly simplifies the multiplier design. The high-bandgap barriers prevent electron transport through the structure so that the depletion region of the modulation layers is controlled by the applied bias, thus modulating the capacitance of the device. By varying the number of barriers and the thickness and doping of the modulation layers, it is possible to tailor the HBV diode for various applications, e.g. power-handling capability and frequency of operation. We present four different InGaAs/InAlAs HBV materials on InP fabricated by MOVPE. Two are designed for high-power, mm-wave applications and the other two are optimised for high efficiency up to submm-wave frequencies. In order to handle high power levels, materials 1816 and 1817 have six barriers and a relatively low doping concentration which results in a high break-down voltage. The measured break-down voltage for 1817 of approximately 52 Volts for a current density of 0,1µA/µm2 is, to the best of our knowledge, the highest value reported for HBVs. Materials 1819 and 1820 have higher doping concentrations and shorter modulation layers to reduce losses and the effect of current saturation, see Table 1. Design methods and predicted RF-performance will be presented.