History of hearing aids
The development of transistors in 1948 by Bell Laboratories led to major improvements to the hearing aid. The transistor was invented by John Bardeen, Walter Brattain, and William Shockley. Transistors were created to replace vacuum tubes; they were small, required less battery power and had less distortion and heat than their predecessor. These vacuum tubes were typically hot and fragile, so the transistor was the ideal replacement.The 1952 Sonotone 1010 used a transistor stage along with vacuum tubes, to extend battery life. The size of these transistors led to developments in miniature, carbon microphones. These microphones could be mounted on various items, even eyeglasses. In 1951, Raytheon manufactured the transistor and was one of the first companies to mass-produce transistors to throughout America. Raytheon realized that their hearing aid only lasted short-term and began to sell the vacuum-tube hearing aids again along with transistor hearing aids.
William Gardner Pfann
Pfann was involved in William Shockley's efforts with Bell Labs to use semiconductors to make devices to replace vacuum tubes. The early efforts used germanium. They made high back-voltage germanium rectifiers in 1945. Pfann devised one of the first point-contact transistors: "Specifically, W.G. Pfann had modified the Western Electric 1N26 shielded point-contact (silicon) diode to include two spring-loaded cat whisker point contacts, making a three-electrode configuration with good electrical amplifying properties. This configuration became known at the Type A transistor." He and Walter Brattain developed the process of "forming" these transistors to make them more uniform. 
Pfann also invented a method of bonding fine gold wires to germanium that made the device functional. "The quiet, unassuming man grew steadily in everyone's esteem as he made one valuable contribution after another to the semiconductor research effort."