# Seventy-Five Years since the Point-Contact Transistor: Germanium Revisited
###### Abstract  
The advent of the point-contact transistor is one of the most significant technological achievements in human history with a profound impact on human civilization during the past 75 years. Although the first transistor was made of germanium it was soon replaced by silicon, a material with lower intrinsic carrier mobilities but with a substantially better native oxide. Interestingly, more than two decades ago, germanium was once again considered as a mainstream microelectronic material, since the introduction of high-\(k\) dielectrics allowed the consideration of channel materials irrespective of the quality of their native oxide. After about 50 years of limited studies on the defect processes in germanium, the community once again focused on its applicability for mainstream electronic applications. Nevertheless, there are some bottlenecks that need to be overcome, and it was the aim of the present review to discuss the progress in the understanding of the defect processes of Ge. G 202212121993 20221221993 2  
[PERSON] and [PERSON] published their findings regarding the invention of the transistor in 1948 [2]. The underlying concept of their work was electron mobility in a semiconductor. Previously, electric current flow had been controlled by fragile glass vacuum tubes, and what was sought was an alternative new device that would be smaller and consume less energy. Tubes had brought on electronic circuits during the first half of the twentieth century and had been employed in the implementation of radio, television, radar, the sound recording and reproduction of long-distance telephone networks, and analog and early digital computers. Transistors exploit the low resistivity of materials, such as silicon and germanium, conduct electric current in the solid state, and the flow can be controlled in useful ways by various means, for example by exposure to an electric field or through doping, i.e., the intentional introduction of impurities into pure semiconductor material in order to modulate its structural and electrical properties. Hence, the coming of the transistor literally revolutionised the electronics industry and effectively introduced the Information Age, where the economy relies primarily on information technology [3]. The first principles of field-effect transistors (FET), i.e., transistors that employ an electric field to control the flow of current in a semiconductor, are traced back to [PERSON]'s work in 1925 [4]. [PERSON], [PERSON] and [PERSON]'s structure faced the problem of surface state, where traps on the semiconductor surface hinder electron mobility. An accidental discovery by [PERSON] and [PERSON] in 1955 that silicon dioxide prevents dopants from diffusing into silicon led, later, in 1956, [PERSON] and [PERSON] to invent the MOSFET, which shares the same principles as the original transistor and solves the surface state problem. The MOSFET transistor has been used extensively in integrated circuits [5] and plays a critical role in today's technological, industrial and market landscape, where the economy is increasingly digitised and \"smart\". Enabling technology such as clean rooms, photolithography and planar process rendered integrated circuit manufacture fast and low cost, and since the early 1970s we have witnessed a proliferation of microprocessors. The MOSFET has been scaled down in size continuously through the years, and while once channel lengths were several micrometres, modern integrated circuits include transistors with channel lengths in the order of 10 nanometres. [PERSON]'s law [6] about chip density, i.e., that the number of semiconductor components that can be included on a chip increases exponentially, though undisputed for a number of years in the semiconductor industry, has recently come under revision [7], and fabrication capabilities and techniques have been taken into consideration.