What is a germanium diode, its basic structure, performance parameters, working principle, application examples, differences and development history between germanium and silicon diodes

Germanium diode is an AT93C66B-SSHM-T diode made of germanium (Ge) material. Germanium is a common semiconductor material with a lower bandgap (about 0.67 eV), which was used earlier than silicon (Si) to manufacture semiconductor devices. Below, we will provide a detailed introduction to the basic structure, performance parameters, working principle, application examples, differences from silicon diodes, and development history of germanium diodes.

1、 Basic structure:

The basic structure of a germanium diode consists of two regions, namely an N-type region and a P-type region. The germanium material in the N-type region is doped with impurities, making it the main source of electron carriers. The germanium material in the P-type region is doped with another impurity, making it the main source of hole carriers. The junction formed between two regions is called a PN junction. The formation of PN junction is achieved by doping an appropriate amount of impurities into germanium material.

2、 Performance parameters:

1. Forward Voltage: Germanium diodes can only conduct under forward voltage, and their conduction voltage is generally 0.2V-0.3V, which is lower than the typical conduction voltage of silicon diodes (about 0.6V).

2. Maximum Reverse Voltage: Germanium diodes should have a certain resistance to breakdown under reverse voltage, and their maximum reverse voltage is generally 30V-60V.

3. Maximum Forward Current: Germanium diodes should have a certain carrying capacity under forward current, and their maximum forward current is generally between 100mA-500mA.

4. Reverse Recovery Time: During the process of a germanium diode transitioning from conduction to cutoff, its PN junction requires a certain amount of time to recover, which is called the reverse recovery time.

3、 Working principle:

The working principle of germanium diodes is similar to that of other diodes. When a forward voltage is applied to the PN junction of a germanium diode, due to the special structure of the PN junction, electrons diffuse from the N-type region to the P-type region, while holes diffuse from the P-type region to the N-type region. This diffusion phenomenon leads to the formation of a depletion layer near the PN junction, where there are almost no freely moving charge carriers. When the forward voltage reaches a certain value, the depletion layer disappears and current begins to flow through the diode, which conducts. When a reverse voltage is applied to the PN junction of a germanium diode, the depletion layer widens, making it almost impossible for current to pass through and the diode turns off.

4、 Application example:

Germanium diodes were widely used in electronic devices in the early days due to their low bandgap and high carrier mobility. Here are several application examples of germanium diodes:

1. RF detector: Germanium diodes can be used as detectors for RF signals, converting them into DC signals.

2. Temperature sensor: Due to the fact that the resistance of germanium diodes varies with temperature, they can be used as temperature sensors.

3. Voltage reference source: Due to the relatively stable forward voltage drop of germanium diodes, it can be used as a voltage reference source.

4. Pulse modulator: Germanium diodes can be used as pulse modulators to convert continuous signals into pulse signals.

5、 The difference between germanium and silicon diodes:

1. Material: Germanium diodes are made of germanium material, while silicon diodes are made of silicon material.

2. Bandgap width: The bandgap width of germanium diodes is about 0.67 eV, while that of silicon diodes is about 1.1 eV. The smaller bandgap width of germanium diodes results in higher conductivity at low voltages.

3. Temperature characteristics: The resistance of germanium diodes varies greatly with temperature, while the resistance of silicon diodes varies less with temperature.

4. Price: Due to the widespread use and mature manufacturing processes of silicon materials, the price of silicon diodes is relatively low, while the price of germanium diodes is relatively high.

6、 Development history:

Early semiconductor devices were mainly manufactured using germanium materials. However, with the development of silicon materials and the maturity of manufacturing processes, silicon diodes have gradually replaced the position of germanium diodes. Silicon materials have a large bandgap and good temperature characteristics, making silicon diodes more suitable for large-scale production and application. Therefore, the application scope of germanium diodes is gradually narrowing, and they are currently mainly used in some special fields, such as electronic devices in high-temperature environments and certain RF applications.