Answer
The answer is Heterojunction Bipolar Transistors (HBTs). HBTs are not credited to Herbert Kroemer's contributions. Kroemer's notable contributions include the development of the double-heterostructure laser, which revolutionized the field of optoelectronics, and his groundbreaking work on heterojunctions and high-speed transistors. These innovations paved the way for significant advancements in the semiconductor industry and electronic devices.