Pzt Ferroelectric Thin Film Integration And Performance Of Algan / Gan Semiconductor Heterostructures

The continuously pursuing of electronic information system on the miniaturization and monolithic has put forward higher request on the size and function of electronic film and its integration devices,therefore promoted the research on the integration of solid state oxide functional materials on semiconductor with carrier transport capacity.Due to its piezoelectric effect, thermoelectric effect, spontaneous polarization effect and etc., PZT has long been one of the most popular ferroelectric materials. As the representative of the third generation semiconductor, GaN owns many outstanding performances, such as high breakdown field, high thermal stability and high electronic saturated drifting velocity. Formed by modulation doped of GaN, AlGaN/GaN has a two-dimensional electron gas (2DEG) with high sheet electron density and mobility, becoming a research hotspot in recent years.In this thesis, the integration of PZT with AlGaN/GaN has been studied. Owing to the large lattice mismatch and different growing environments, MgO buffer layer has been introduced to obtain the preferred orientation growth of (111)PZT film. A metal-ferroelectric-insulter-semiconductor structure(MFIS) was fabricated through microfabrication. By the capacitance-voltage(C-V) and leakage current-voltage(I-V) measurement, the electronic properties of MFS and MFIS was studied.Firstly, the PZT film was prepared on Al₂O₃, which has similar crystal structure with GaN. XRD scan shows that PZT film grown directly on AlGaN/GaN was polycrystal, and there were holes and defects on the surface from AFM results. The preferred orientation growth of (111)PZT film could be realized by inserting MgO buffer layer, the crystallization quality was improved.Then,PZT film was deposited on AlGaN/GaN, highly oriented (111)PZT was observed with MgO buffer layer.φscan indicated the epitaxial relationship of (111)[1-10]PZT // (0002)[11-20]GaN.PZT film shows double domain structure.After the fabrication of MFIS, C-V properties were studied. The results showed counterclockwise hysteresis induced by ferroelectric polarization as MgO buffer was bung in. With increasing the positive bias the window of the counterclockwise hysteresis increased. When V_max=2V, both the V_window and theΔn_s reached maximum, 0.5V and 3.49×1011/cm2.However, both the V_window andΔn_s decrease with further increasing V_max. These results indicated the modulation of the switchable ferroelectric polarization on 2DEG. And the memory window increases to 0.7V as the thickness of the buffer layer decreases to 2nm,the threshold voltage(V_th) move towards the positive direction to -1.7V.The gate control ability was increased. The leakage current density of MFIS has been reduced by five orders of magnitude.