ABSTRACT
Binary-phase diagrams are most commonly used in the study of metal and semiconductor material systems. Figure 3.1 shows a hypothetical diagram for explaining the terminology. The two components A and B are the ends of the x axis. The y axis is the temperature. Pressure is set to 1 atm. At the two ends, close to pure A or B, as the temperature goes up, the solid phase (a or b) changes to liquid as it crosses the liquidus line. At any composition (% A), as the temperature goes up, the solid phase changes to a mixture of either phase, including the liquid phase, and then to just the liquid phase. The lowest melting point is seen at point E, the eutectic point.
3.1.2.1 Isomorphous phase diagramThis type of phase diagram is shown in Fig. 3.2, which shows the phase diagram for the GaAs-GaP system [3, 1]. This type of diagram is characteristic of materials that are completely soluble in each other. Ga being common, As and P occupy the group V sites randomly, the atomic radii being within 15% of each other. Si and Ge form a similar phase diagram. For such material combinations, other properties may vary monotonically also, such as energy bandgap, lattice constant, etc.
