## 1 Introduction  
Temperature-induced amorphous and crystalline states of a phase change material (PCM) possess two distinct energy band structures; hence, they have different physical and chemical properties [1]. One such property is reflectivity, which has been utilized in the optical storage industry for storing data in the form of CDs and DVDs [2]. Similarly, a large difference (4-6 orders of magnitude) in resistance (hence the resistivity) values in amorphous and crystalline phases of a PCM is the basis for next generation non-volatile memory applications [3]. Furthermore, the ability to switch from a highly resistive amorphous state (OFF) to a highly conductive crystalline state (ON) or vice-versa makes PCM an ideal candidate for radio-frequency (RF) switching applications [4]. In previous works, thermal-induced reversible phase transition has been demonstrated in several chalcogenide compounds such as germanium antimony telluride (GeSbTe or GST), and germanium telluride (GeTe) [4; 5; 6]. For example, [PERSON] et al. demonstrate Joule heating induced phase transition in GST electronic memory cells of size \(\sim\)0.80 \(\upmu\)m \(\times\) 0.40 \(\upmu\)m \(\times\) 60 nm and concluded that the threshold switching in such devices does not depend on structural changes [7]. In fact, it was an outcome of competition between trap-assisted carrier recombination and field-assisted carrier generation. In the same work, it was also observed that the PCM crystallization depends not only on the magnitude but also on the duration of applied current pulse [7]. However, poor thermal stability in amorphous phase GST and void formation due to volume shrinkage upon crystallization limit the GST application range [8]. In comparison to GST, GeTe has several advantages including higher stability in amorphous phase, ultra-fast reversible phase transition (\(\upmu\)s-to crystallize and ns-to amorphized), and higher OFF/ON resistivity ratio. All these superior properties make GeTe a leading candidate for memory, as well as RF switching applications [9]. The main advantages of GeTe RF switches over the conventional microelectromechanical systems (MEMS) electrostatic switches (of the same size) are, including but not limited to the simpler fabrication method, long lifetime, large cut-off frequency (in THz), near zero in-state power consumption/lower switching voltages, high power handling capabilities, immune to radiation exposure (good for space applications), and the elimination of special packaging requirements [9; 10; 11; 12; 13]. Furthermore, the simpler design allows the integration of GeTe switches with various MEMS and CMOS devices. As the properties of PCM depend on the nature of the transition (sharpness, duration etc. ), it is important to understand the phase change mechanism for fabricating the GeTe RF switches of desired properties. The transition between insulating (amorphous) and conducting (crystalline) phases is usually induced by heating and cooling the PCM resistor. When room temperature-grown PCM (in amorphous phase) is heated uniformly above its glass temperature (T\({}_{\mathrm{g}}\)), crystallization occurs. In the case of GeTe thin films, crystallization starts with the growth of small nuclei followed by their continuous expansion until they merge with other crystal sites to form larger crystals [14]. On the other hand, the transition from the crystalline to the amorphous phase occurs upon quenching the PCM material from its melting point (T\({}_{\mathrm{M}}\)). The quenching/heating rate, minimum/maximum temperature, heating methods, and even the device size and geometry are some of the parameters that decide the switching time and behavior. Two most common heating methods, Joule and indirect thermal heating, are in use to induce phase transition in GeTe devices [15]. In the indirect heating method, a separate resistive heater near to the PCM resistor provides enough heat for the phase transition, whereas Joule heating involves drawing current directly through the PCM.