Design and characterization of n -Si/p -CdO broken gap heterojunctions as high frequency PMOSFETs and microwave resonators

Abstract

Herein, 𝒑−type CdO thin films coated onto 𝒏−type Si crystals are employed to form metal oxide semiconductor field effect transistors (MOSFET). In the broken gap design, the valence band edge of Si substrates centered at 5.25 eV is aligned at conduction band edges of CdO centered at 5.20 eV. The construction of the energy band diagram indicated that the devices could reveal a deep built in potential of 4.68 eV. The device is fabricated by the thermal evaporation technique under vacuum pressure of 10-5 mbar. CdO thin films grown onto Si thin crystals form a randomly distributed nanorod-like grains of rod length and diameter of ~2.0 𝝁𝒎 and 160 nm, respectively. In addition, 𝒏−Si/𝒑−CdO heterojunctions displayed typical diode characteristics with ideality factors of ~1.40 and barrier height of 0.67 eV. As passive mode devices, the C-V curves displayed enhanced PMOS channel with the ability of capacitance depletions in a wide range of frequency (10M-1.0 GHz). The depletion width of the device widens from 7.0 nm to 660 nm in that frequency domain. Moreover, the biased and unbiased impedance spectra analyses in the frequency domain of 1.0M-1.0 GHz, indicated the voltage controllability of the devices when operated as microwave cavities. The magnitude of the reflection coefficient spectra indicated the ability of using the MOSFET devices as high pass filters. The features of the 𝒏−𝐒𝐢/𝒑-CdO heterojunctions nominate them for use as microwave band filters, PMOS field effect transistors and as frequency and voltage controlled tunable capacitors