Translation of an article by authors from IBM Research.
An important breakthrough in physics will allow us to study the physical characteristics of semiconductors in much greater detail. Perhaps this will help accelerate the development of next-generation semiconductor technology.
Authors:
β Staff Member, IBM Research
Doug Bishop - Characterization Engineer, IBM Research
Semiconductors are the basic building blocks of today's digital, electronic age, providing us with a variety of devices that bring benefits to our modern lives, such as computers, smartphones and other mobile devices. Improvements in semiconductor functionality and performance also enable next-generation semiconductor applications for computing, sensing, and power conversion. Researchers have long struggled to overcome the limitations of our ability to fully understand the electronic charges within semiconductor devices and advanced semiconductor materials that are holding us back from moving forward.
In a new study in the journal A research collaboration led by IBM Research describes an exciting breakthrough in unlocking a 140-year-old mystery in physics, one that will allow us to study the physical characteristics of semiconductors in much greater detail and enable the development of new and improved semiconductor materials.
To really understand the physics of semiconductors, we must first know the fundamental properties of charge carriers within materials, whether they are negative or positive particles, their speed in an applied electric field, and how densely packed they are in the material. Physicist Edwin Hall found a way to determine these properties in 1879 when he discovered that a magnetic field will deflect the movement of electronic charges within a conductor, and that the magnitude of the deflection can be measured as the potential difference perpendicular to the directed flow of charged particles, as shown in Figure 1a. This voltage, known as the Hall voltage, reveals meaningful information about the charge carriers in a semiconductor, including whether they are negative electrons or positive quasi-particles called βholesβ, how fast they move in an electric field, or their βmobilityβ (Β΅) , and their concentration (n) inside the semiconductor.
140 year secret
Decades after Hall's discovery, researchers also found they could measure the Hall effect with lightβexperiments called photo-Hall, see Figure 1b. In such experiments, light illumination generates multiple carriers or electron-hole pairs in semiconductors. Unfortunately, our understanding of the main Hall effect provided insight into only the majority charge carriers (or majority carriers). The researchers were unable to extract the parameters of both carriers (primary and non-primary) at the same time. Such information is key to many light-related applications such as solar panels and other optoelectronic devices.
An IBM Research study in a journal reveals one of the long-kept secrets of the Hall effect. Researchers from the Korea Advanced Institute of Science and Technology (KAIST), Korea Research Institute of Chemical Technology (KRICT), Duke University, and IBM have discovered a new formula and technique that allows us to simultaneously extract information about the majority and non-major carriers, such as their concentration and mobility, as well as obtain additional information about the lifetime of the carrier, diffusion length and the recombination process.
More specifically, in the photo-Hall experiment, both carriers contribute to changes in the conductivity (Ο) and the Hall coefficient (H, proportional to the ratio of the Hall voltage to the magnetic field). Key insights come from measuring conductivity and the Hall coefficient as a function of light intensity. Hidden in the shape of the curve, the conductivity-Hall coefficient (Ο-H) reveals fundamentally new information: the difference in the mobility of both carriers. As discussed in the article, this relationship can be expressed elegantly:
$$display$$ ΞΒ΅ = d (ΟΒ²H)/dΟ$$display$$
Starting from the known majority carrier density from the traditional Hall measurement in the dark, we can reveal both majority and minority carrier mobility and density as a function of light intensity. The team called the new measurement method Carrier-Resolved Photo Hall (CRPH). With a known intensity of light illumination, the lifetime of the carrier can be determined in a similar way. This connection and related solutions have been hidden for almost a century and a half, since the discovery of the Hall effect.
In addition to advances in this theoretical understanding, advances in experimental methods are also critical to enabling this new method. The method requires a pure measurement of the Hall signal, which can be difficult for materials where the Hall signal is weak (for example, due to low mobility) or when there are additional unwanted signals, as with strong light irradiation. To do this, it is necessary to perform a Hall measurement using an oscillating magnetic field. As with listening to the radio, you must select the frequency of the desired station, discarding all other frequencies that act as noise. The CRPH method goes one step further and selects not only the desired frequency but also the phase of the oscillating magnetic field in a method called synchronous detection. This concept of oscillating Hall measurement has been known for a long time, but the traditional method of using a system of electromagnetic coils to generate an oscillating magnetic field was inefficient.
Previous discovery
As is often the case in science, advances in one area are driven by discoveries in another. In 2015, IBM Research reported on a previously unknown phenomenon in physics associated with a new magnetic field confinement effect called the βcamel humpβ effect that occurs between two lines of transverse dipoles when they exceed a critical length, as shown in Figure 2a. The effect is a key feature that provides a new type of natural magnetic trap called a parallel dipole line trap (PDL trap), as shown in Figure 2b. The magnetic PDL trap can be used as the latest platform for a variety of sensor applications such as inclinometer, seismometer (earthquake sensor). These new sensor systems, together with big data technologies, could open up many new applications, and are being explored by the IBM Research team developing a big data analytics platform called the IBM Physical Analytics Integrated Repository Service (PAIRS), which hosts a wealth of geospatial and IoT data. (IoT).
Surprisingly, the same PDL element has another unique use. When rotated, it serves as an ideal system for the photo-hall experiment to obtain a unidirectional and pure harmonic oscillation of the magnetic field (Figure 2c). More importantly, the system provides enough space to allow illumination of a large area of ββthe sample, which is critical in photo-Hall experiments.
Impact
A new photo-Hall technique has been developed that allows us to extract an amazing amount of information from semiconductors. Unlike only three parameters obtained in the classical Hall measurement, this new method yields up to seven parameters at each of the tested light intensities. This includes the mobility of both electrons and holes; the concentration of their carrier under the influence of light; recombination lifetime; and the diffusion length for electrons, holes, and the ambipolar type. All this can be repeated N times (i.e. the number of light intensity parameters used in the experiment).
This new discovery and technology will help advance semiconductor advances in both existing and emerging technologies. We now have the knowledge and tools needed to extract the physical characteristics of semiconductor materials in great detail. For example, it will help accelerate the development of next-generation semiconductor technology, such as better solar panels, better optoelectronic devices, and new materials and devices for artificial intelligence technologies.
articles published on October 7th, 2019 in .
Translation: Nikolai Marin (), Chief Technology Officer of IBM in Russia and CIS countries.
Source: habr.com