**2. Material parameter and design consideration of Si, GaAs IMPATT diodes**

The material parameters take the vital role for the design of the diodes as well as the IMPATT operation. We have used the values of material parameters of the semiconductors under consideration i.e. the carrier ionization rate, saturation drift velocity of electron (*v*sn), and hole (*v*sp), mobility (*μ*), permittivity (εs) etc. obtained from the research reports [17–26]. The material parameters used for the computer simulation IMPATT diodes based on the semiconductors concerned are summarized in **Table 1**. Besides theses parameters for IMPATT it is required to consider about the diode area, junction temperature and the operating current density at the desired design frequency. In this case we have taken the uniform diode area and junction temperature, but the current density is taken as per the operating frequency.

*IMPATT Diodes Based on GaAs for Millimeter Wave Applications with Reference to Si DOI: http://dx.doi.org/10.5772/intechopen.95874*


#### **Table 1.**

*Material parameters of Si and GaAs semiconductors.*

To design an IMPATT diode one needs to consider its efficiency, frequency of operation, low cost, low loss thermal and electrical constants, output power and it is also important to achieve the breakdown condition for IMPATT operation. Energy band gap, ionization rate, dielectric constant, thermal conductivity, saturation drift velocity of electron and hole and break down field are the key factors to acquire the simulation results of efficiency, breakdown voltage and the output power of IMPATT. Taking into account the suitability of all these material properties, we have used the design criteria as W = 0.5 vsn,sp/fd; where W, vsn,sp and fd are the total depletion layer width, saturation velocity of electrons and design operating frequency respectively and chosen the double drift region (DDR) optimized structure to explore the potential of GaAs IMPATT diode. The schematic diagram of the DDR structure is shown in **Figure 1**. This structure depends on the saturation velocity and design operating frequency.

The diodes have the doping distribution of the form n<sup>+</sup> npp<sup>+</sup> and are designed to operate at a frequency of 94, 140 and 220 GHz. Each n and p-region has width as well as the total width for the active region which has been mentioned in the **Table 2**. The width of the n<sup>+</sup> and p<sup>+</sup> are negligible and are hence used for ohmic contacts. The doping concentration for each n and p region of all structures have been mentioned in **Table 2**, while the doping concentration for each n<sup>+</sup> and p+ region are taken as 1.0 × 1026 m−3. The optimized operating current density, junction temperature and diode area are taken for window frequency of 94 GHz, 140 GHz and 220 GHz and listed in **Table 2**. Again the junction temperature and diode area are taken as 300 K and 1.0 × 10−10 m2 respectively.

Though the applications of IMPATT diode are mostly realized on the basis of double drift region structures, we have considered the symmetrical double drift region (DDR) IMPATT diode structures with doping distribution of the form n<sup>+</sup> npp<sup>+</sup> as shown in **Table 2** for the DC, small signal and noise analysis. 1-D schematic diagram of the proposed DDR IMPATT diode structures are shown in **Figure 1**. The n<sup>+</sup> and p<sup>+</sup> regions of the diode are heavily doped with each having a doping concentration of 1.0 × 1026 m−3. Each n- and p-regions has a moderate doping concentration for different materials based on the optimized current

## **Figure 1.**

*A 1-D schematic diagram of the proposed DDR IMPATT diode.*


#### **Table 2.**

*Design parameters of Si and GaAs DDR IMPATT.*

density as given in **Table 2**. The total active regions width is taken along with different space points of 1 nm each on both p-region and n-region. The values of doping concentrations and diode active region width are taken for optimum conversion efficiency and operation at atmospheric window frequencies of 94 GHz, 140 GHz and 220 GHz. The net doping concentration at any space point is hence determined by using the exponential and error function profiles.
