Heterojunctions refer to the interface formed between two different semiconductor materials, each with different band gaps and properties. These junctions play a crucial role in a wide range of electronic and optoelectronic devices, including transistors, light-emitting diodes (LEDs), solar cells, and lasers. By combining materials with complementary properties, heterojunctions can be engineered to improve device performance, efficiency, and functionality. Research in this area focuses on understanding the electronic and optical properties of heterojunctions, designing novel materials combinations, and developing new fabrication techniques for advanced devices.