How can you distinguish between germanium diodes and silicon diodes?

SiC Schottky diodes can be widely used in medium- and high-power applications such as switch-mode power supplies, power factor correction (PFC) circuits, uninterruptible power supplies (UPS), and photovoltaic inverters, significantly reducing circuit losses and increasing operating frequencies. In PFC circuits, replacing conventional silicon FRDs (fast recovery diodes) with SiC SBDs (Schottky barrier diodes) enables operation at frequencies above 300 kHz while maintaining nearly constant efficiency, whereas circuits using silicon FRDs at frequencies above 100 kHz experience a sharp decline in efficiency. As the operating frequency increases, the size of passive components such as inductors decreases accordingly, resulting in an overall reduction of more than 30% in the PCB footprint.

In Electronic In electronics, diodes possess the unique property of unidirectional conduction. Their primary functions include rectification, voltage regulation, and detection. Additionally, light-emitting diodes (LEDs) made from various materials are incorporated for signaling and illumination. In diodes circuit In a diode, current can flow only from the anode to the cathode. Depending on circuit requirements, numerous types of diodes are available. Most early diodes were fabricated from single-crystal germanium. Later, with advances in silicon materials and manufacturing techniques, silicon diodes were developed and widely adopted. The following outlines how to distinguish between silicon (Si) diodes and germanium (Ge) diodes.

I. Circuit Characteristics: Silicon and Germanium Transistors
1.1 Differences Between Germanium Diodes and Silicon Diodes
Silicon diodes and germanium diodes have identical circuit characteristics and are manufactured using the same processes. However, due to their different materials, silicon diodes exhibit superior thermal stability, whereas germanium diodes have somewhat poorer thermal stability.
(1) At the same current, the DC resistance of a Ge diode is lower than that of a Si diode. However, for AC resistance, the situation is exactly the opposite.

(2) According to experimental studies, a Ge diode begins to conduct at a forward voltage of 0.2 V, whereas an Si diode does not begin to conduct until 0.5 V; in other words, the two diodes have different threshold voltages for conduction.
(3) Under reverse bias, the leakage current of a silicon diode is much smaller than that of a germanium diode. Once conduction begins, the current in a germanium diode increases slowly, whereas the current in a silicon diode rises relatively more rapidly.
(4) The threshold voltage of a silicon transistor is higher than that of a germanium transistor, because the threshold current of a silicon transistor is much smaller than that of a germanium transistor. Typically, the threshold voltage of a silicon transistor is about 0.5 V to 0.6 V, whereas that of a germanium transistor is about 0.1 V to 0.2 V.
(5) Temperature variations have a significant impact on germanium diodes but only a minor effect on silicon diodes. Consequently, silicon diodes exhibit superior high-temperature performance compared to germanium diodes.

As shown in the table above, the forward voltage required to turn on a silicon diode is higher than that of a germanium diode; therefore, by measuring the forward voltage, one can distinguish between the two types of diodes.

In addition, there is a very straightforward method for measuring diodes using the ohmmeter range of a multimeter. As shown in the figure, connect the multimeter’s red probe (anode) to the diode’s cathode and the black probe (cathode) to the diode’s anode. If the measured resistance is around 1 kΩ, the diode is a germanium device; if the resistance is 4–8 kΩ, it is a silicon device.

Compared with germanium diodes, silicon diodes offer higher breakdown voltage, faster response times, and more stable performance. In most circuits, silicon diodes can replace germanium diodes, but their forward voltage drop is higher. Consequently, in certain specific applications—such as small-signal detection circuits—germanium diodes are preferable.

1.2 Differences between Ge and Si Transistors
The main difference lies in their forward voltage drops: germanium diodes have a lower forward voltage of about 0.3 V, whereas silicon diodes exhibit a higher forward voltage of approximately 0.7 V. Moreover, silicon is abundant and its fabrication processes are well-suited for mass production, which has led to its widespread use as the primary component in electronic devices.
Germanium Semiconductor The material exhibits high electron mobility, making it suitable for low-voltage, high-current devices; however, its temperature characteristics are inferior to those of silicon. The reverse leakage current of a PN junction is significantly higher than that of silicon. Consequently, silicon devices must be employed in high-power applications and circuits with high reverse‑bias voltages.
A bipolar transistor has two PN junctions. With respect to these junctions, the forward voltage of a germanium transistor’s PN junction is as low as 0.3 V, whereas that of a silicon transistor is 0.7 V. Germanium transistors have very low reverse breakdown voltages, making them prone to reverse breakdown. Consequently, germanium transistors exhibit relatively large leakage currents, which can introduce noise into amplifier circuits and lead to device failure.

1.3 
Germanium diodes were widely used in early electronic devices, such as radios, but they have largely been replaced by silicon diodes. This is because the crystal structure of germanium is easily disrupted at higher temperatures, whereas silicon crystals are much more resistant to thermal damage. Moreover, silicon diodes typically offer a higher peak reverse‑voltage rating than germanium diodes. In addition, silicon is inexpensive to produce and lends itself readily to high‑quality silicon dioxide through impurity diffusion and surface‑passivation processes. Consequently, germanium diodes were manufactured only until the 1970s.

II. Common Types and Applications of Diodes
(1) Zener diode Zener diode
It is also made of a PN structure. During operation, it remains in the reverse breakdown region (where a conventional diode would be damaged). When connecting it to a circuit, the polarity must be reversed: the anode of the Zener diode should be connected to the cathode of the voltage‑regulation circuit, and the same applies to the other terminals. By exploiting the fact that the reverse breakdown current varies over a wide range while the reverse breakdown voltage remains essentially constant, the Zener diode achieves voltage regulation.
(2) Light-emitting diode Light-emitting diode
It emits light when forward current passes through it, exhibiting electro‑optical conversion. Visible light encompasses red, yellow, green, blue, violet, and other colors. It is widely used in various electronic devices as an indicator of operating status.
(3) Photodiode Photodiode

The main feature is that the lamp operates in reverse bias, with the reverse current being directly proportional to the illuminance.
(4) Automobile
Using rectifier diodes: The operating principle of silicon rectifier diodes used in automotive alternators is essentially the same as that of other diodes, but their external structure differs from standard diodes. Each diode has one lead as the anode and the other as the cathode; it is housed in a metal case. These diodes are classified into positive‑type and negative‑type. In the positive‑type diode, the terminal is the anode and the case is the cathode, whereas in the negative‑type diode, the front terminal is the cathode and the case is the anode. For easy identification, the positive‑type diode is typically marked with a red dot, while the negative‑type diode is marked with a black dot.
(5) Freewheeling Diode Freewheeling Diode

It is commonly found in automobiles. In addition, fast-recovery diodes—semiconductor diodes with excellent switching characteristics and short reverse‑recovery times—are primarily used as switching devices in various power converters (such as IGBTs or MOSFETs) to provide freewheeling current.
Silicon Carbide Schottky Diode
4.1 Basic Type of Silicon Carbide Schottky Diode
Schottky diodes, also known as hot-carrier diodes, achieve rectification by forming a Schottky barrier at the metal–semiconductor junction. Compared with conventional PN-junction diodes, they exhibit very low reverse‑recovery charge. Consequently, Schottky diodes are well suited for high‑frequency rectification or high‑speed switching.
Silicon carbide (SiC) is a high-performance semiconductor material; accordingly, SiC Schottky diodes offer higher energy efficiency, greater power density, smaller form factors, and enhanced reliability. They are well suited for power electronics, pushing beyond the limitations of silicon and emerging as the optimal device for next-generation energy systems and power electronics applications.

4.2 Technical Characteristics of Silicon Carbide
SiC is a compound semiconductor composed of silicon and carbon. Compared with silicon, it offers numerous advantages. SiC’s bandgap is 2.8 times that of silicon (a wide bandgap), reaching 3.09 eV. Its dielectric breakdown field strength is 5.3 times that of silicon, up to 3.2 MV/cm, and its thermal conductivity is 3.3 times that of silicon, approximately 49 W/cm·K. Like silicon, it can be used to fabricate junction devices, field-effect devices, and specialized Schottky diodes. The following are the key characteristics of silicon carbide:
(1) Silicon carbide single‑carrier devices feature a thin drift region and low on‑state resistance, which is approximately 100–300 times lower than that of silicon devices. Thanks to their low on‑state resistance, silicon carbide power devices exhibit reduced forward conduction losses.
(2) Silicon carbide power devices exhibit high breakdown voltages due to their high breakdown electric field. For example, commercial silicon Schottky diodes typically have voltage ratings below 300 V, whereas the first commercially available SiC Schottky diode already achieved a breakdown voltage of 600 V.
(3) Silicon carbide exhibits high thermal conductivity.
(4) SiC devices can operate at higher temperatures, whereas the maximum operating temperature of Si devices is only 150ºC.
(5) Silicon carbide exhibits excellent radiation resistance.
(6) The forward and reverse characteristics of SiC power devices exhibit little variation with temperature and time, resulting in excellent reliability.

(7) SiC devices exhibit excellent reverse recovery characteristics, with low reverse recovery current and reduced switching losses.
(8) SiC devices can reduce the size of power devices and lower circuit losses.
4.3 Applications of Silicon Carbide Schottky Diodes
SiC Schottky diodes can be widely used in switching applications. Power supply In high- and medium-power applications such as power factor correction (PFC) circuits, uninterruptible power supplies (UPS), and photovoltaic inverters, it can significantly reduce circuit losses and increase the operating frequency.
In a PFC circuit, replacing the conventional silicon FRD (fast recovery diode) with a SiC SBD (Schottky barrier diode) enables operation at frequencies above 300 kHz while maintaining nearly constant efficiency, whereas circuits using silicon FRDs at frequencies above 100 kHz experience a sharp drop in efficiency. As the operating frequency increases, passive components such as inductors… Component Its volume is correspondingly reduced, resulting in a more than 30% reduction in the overall circuit board’s volume.