Why Early Transistor Manufacturers Switched from Germanium

During the dawn of the solid-state electronics era in the late 1940s and early 1950s, germanium was the primary material used to manufacture transistors. However, despite its initial success, germanium presented severe limitations that hindered the advancement of modern computing and reliable electronics. Early manufacturers quickly transitioned from germanium wafers to silicon due to germanium's poor thermal stability, the inferiority of its native oxide for manufacturing, its scarcity and high cost, and high leakage currents. Overcoming the initial hurdles of purifying silicon allowed the electronics industry to build the reliable, mass-produced microchips that power the modern world.

Thermal Sensitivity and Bandgap Limitations

The most critical flaw of germanium was its inability to handle heat. In physics, a semiconductor's reliability at high temperatures is determined by its "bandgap"—the energy required to free an electron so it can conduct electricity. Germanium has a relatively small bandgap of 0.67 electron volts (eV), whereas silicon has a much wider bandgap of 1.12 eV.

Because of its narrow bandgap, germanium transistors suffered from "thermal runaway." When a germanium device operated, it generated heat. This heat freed more electrons, which increased the electrical current, subsequently generating even more heat. At temperatures above 75°C (167°F), germanium transistors simply stopped functioning and often destroyed themselves. Silicon, by contrast, could easily operate at temperatures up to 150°C (302°F) or higher, making it mandatory for military, aerospace, and heavy industrial applications.

High Leakage Currents

Closely related to its thermal issues was germanium's high leakage current. Even when a transistor is switched "off," a tiny amount of electrical current still leaks through it. Germanium's material properties caused it to have a significantly higher leakage current than silicon. This made germanium circuits power-inefficient and unpredictable, especially as engineers tried to pack more transistors into smaller spaces. Silicon provided a much tighter "off" state, ensuring reliable performance in complex logic circuits.

The Oxide Advantage and the Planar Process

For manufacturers, the chemical properties of a wafer's surface are just as important as its electrical properties. To build integrated circuits, manufacturers need an insulating layer on top of the semiconductor wafer to protect it from contamination and to etch microscopic pathways.

When silicon is heated in the presence of oxygen, it naturally grows a layer of silicon dioxide (essentially glass). Silicon dioxide is chemically stable, non-water-soluble, and a phenomenal electrical insulator. Conversely, germanium forms germanium dioxide, which is water-soluble and chemically unstable. It easily washes away during the chemical baths required in wafer fabrication. The stability of silicon dioxide enabled the invention of the "planar process" in 1959, which allowed manufacturers to print entire circuits onto a single wafer, paving the way for the microprocessor.

Material Scarcity and Supply Chain Costs

Economics also drove the transition. Germanium is a relatively rare element, typically obtained as a byproduct of zinc ore processing and coal fly ash. As the demand for transistor radios, computers, and defense systems exploded in the 1950s, the high cost and limited supply of germanium became a major bottleneck.

Silicon is the second most abundant element in the Earth's crust, readily available in ordinary sand and quartz. While silicon requires much higher temperatures to melt and purify than germanium—a hurdle that kept germanium in the lead initially—metallurgists perfected silicon purification techniques by the mid-1950s. Once the refining process was mastered, the raw material cost for silicon wafers plummeted, making mass production economically viable.