Metal-oxide-semiconductor field-effect transistors (MOSFETs) are basic to modern electronics. They work in enhancement or depletion modes, showing unique features. The key differences include how the channel is made, the threshold voltage, biasing needs, and switching properties.
Enhancement mode MOSFETs are off by default. They don’t let current pass from source to drain without a gate voltage. In contrast, depletion mode MOSFETs are on by default. They already have a path for current, enabling flow without a gate voltage. Enhancement mode needs a positive gate voltage to turn on. But, depletion mode can turn off a current path with the gate’s negative voltage.
Understanding the differences between n-channel depletion mode, p-channel depletion mode, n-channel enhancement mode, and p-channel enhancement mode MOSFETs is key. It helps in creating efficient electronic circuits.
Understanding MOSFET Operating Modes
MOSFETs work in two main ways: enhancement and depletion. It’s key to know how these MOSFET operating modes differ. This helps in picking the right one for a task.
Enhancement Mode MOSFETs
Enhancement mode MOSFETs are “off” until given a positive gate voltage (VGS). To start them up, a voltage above their threshold is needed. This allows them to let current pass between their source and drain.
Depletion Mode MOSFETs
Depletion mode MOSFETs act the opposite. They naturally let current through without a gate voltage. To stop this current flow, the gate gets a reverse-type voltage. This process closes off the channel, no longer letting current flow.
Normally On vs. Normally Off Devices
Depletion mode MOSFETs are normally ready to conduct. They don’t need a gate signal to start working. This makes them “normally on”. Enhancement mode MOSFETs are the opposite. They need an initial gate voltage to start passing current. This makes them “normally off”.
Key Differences Between Enhancement and Depletion Mode MOSFETs
The first source highlights the main differences between enhancement mode and depletion mode MOSFETs. They mainly vary in how their channels form, the threshold voltage needed, how they are biased, and their switching actions.
Enhancement mode MOSFETs start without a channel. They need a certain gate voltage to create the channel and begin conducting. In contrast, depletion MOSFETs begin with a channel that can be shrunk by a certain gate voltage. This lets them work in more modes than enhancement MOSFETs.
The difference in threshold voltage is also key. For enhancement devices, a specific gate voltage above the threshold starts conduction. In depletion mode, though, the device conducts without needing this threshold voltage.
Biasing needs are varied between the two. To turn off a depletion MOSFET, you apply a specific opposite-gate voltage. Enhancement MOSFETs need a gate bias in the right direction to start conducting.
In summary, the distinction in how channels create, threshold voltage needs, biasing, and switching sets them apart. These play a significant role in where and how these MOSFETs are used.
Channel Formation and Conduction
Enhancement and depletion MOSFETs differ in how their conductive channels form. Depletion mode MOSFETs come with a channel ready to go. This allows them to let current flow from the source to the drain without needing a gate voltage. On the other hand, enhancement mode MOSFETs need help forming their channel. They can’t conduct until a gate voltage is applied to them.
Depletion mode MOSFETs are always ready to conduct. Their channel is set up during manufacturing. So, they can pass current without an additional voltage. But, for enhancement mode MOSFETs to conduct, a gate voltage must turn on their channel first.

The way the conductive channels are formed marks a big difference. It’s a crucial point that separates enhancement and depletion mode MOSFETs. Understanding this helps to get how each type works and what they’re used for.
Threshold Voltage and Biasing
The threshold voltage is crucial for enhancement and depletion mode MOSFETs. Enhancement mode devices need to pass a certain voltage to turn on. They allow conduction between source and drain only after reaching this voltage.
Depletion mode MOSFETs are always ready to conduct without an extra voltage. This makes them different from enhancement mode MOSFETs.
Threshold Voltage in Enhancement Mode
For enhancement mode MOSFETs, the threshold voltage is key. It’s the lowest gate-to-source voltage needed to let current flow. This voltage is different for n-channel and p-channel devices.
A positive threshold voltage turns on n-channel devices, while a negative one turns on p-channel devices. After this, current can flow through the device.
Biasing Depletion Mode MOSFETs
Depletion mode MOSFETs turn off using an opposite gate voltage. For n-channel devices, a negative voltage stops the current. For p-channel devices, a positive voltage does the same job.
Biasing Enhancement Mode MOSFETs
To activate enhancement mode MOSFETs, you need a forward bias. This means applying the right gate voltage. For n-channel, it’s a positive voltage. For p-channel, it’s a negative one.
N-Channel and P-Channel Characteristics
In the world of MOSFETs, n-channel and p-channel devices are key. Both types, n-channel and p-channel, can be either depletion or enhancement. Each has its own special features and uses.
N-Channel Depletion Mode
N-channel depletion mode MOSFETs work with a negative gate-source voltage. They have an n-type channel and a p-type substrate. Because of this, they’re naturally on, allowing current to flow between the source and drain without gate voltage.
P-Channel Depletion Mode
On the other hand, p-channel depletion mode MOSFETs need a positive voltage to cut their current. They use a p-type channel and an n-type substrate. They share a feature with n-channel devices by being naturally in a conductive state.
N-Channel Enhancement Mode
N-channel enhancement mode MOSFETs differ as they start off not conducting. They work with a positive gate voltage. This gate voltage turns them from “off” to “on”, allowing current to flow.
P-Channel Enhancement Mode
P-channel enhancement mode is the opposite and needs a negative gate voltage. They create an p-type channel to let current flow between the source and drain. Like n-channel enhancement devices, they start in a non-conductive state.
MOSFET Switching and Operation
The switch on and off of depletion and enhancement MOSFETs is key to how they work. Depletion mode MOSFETs are always conducting unless the gate voltage stops them. To pause the flow, a gate voltage of the opposite sort is needed to close the channel that allows current.
Switching On Depletion Mode MOSFETs
Depletion mode MOSFETs are usually conducting without a gate voltage. Turning them off needs this reverse voltage. It stops the current by reducing the number of current carriers in the channel.
Switching On Enhancement Mode MOSFETs
Enhancement mode MOSFETs act in the opposite way. They need the proper gate voltage to start conducting. This happens when the VGS is big enough to overcome the VTH.
For n-channel enhancement MOSFETs, a positive gate voltage opens up a channel. For p-channels, it’s a negative one. This allows current to flow between the source and the drain.

Applications and Use Cases
When choosing between enhancement mode MOSFETs and depletion mode MOSFETs, it all comes down to the job. Enhancement mode devices work well in small power needs. They stay off by default. Depletion mode MOSFETs fit better in tasks where a power flow is needed, like in H-bridge setups.
Integrated circuits often mix both types of transistors. Yet, the first source’s authors haven’t seen much use of depletion types. This hints that MOSFET applications lean towards the enhancement kind. The cited researchers’ experience points in this direction.
Application | Enhancement Mode MOSFET | Depletion Mode MOSFET |
---|---|---|
Low-power Switching | Commonly Used | Less Suitable |
H-bridge Configurations | Less Suitable | May be Used |
Integrated Circuits | Widely Adopted | Less Prevalent |
Semiconductor Device Physics
Semiconductor device physics is crucial for Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs). MOSFETs are the heart of today’s electronic circuits. They depend on how electrons and holes move, which affects the devices differently.
Charge Carrier Behavior
MOSFET operation is all about managing the movement of electrons and holes. This is key for the devices to work well. The way charge carriers act impacts how MOSFETs turn on and off.
Gate Oxide Insulation
The gate oxide layer is also very important in MOSFETs. It’s a super-thin, insulating layer between the gate and the channel. This layer allows the MOSFET to work without direct touch. The layer’s properties greatly affect how the MOSFET performs and switches on and off.
Comparison Table: Depletion vs. Enhancement Mode
There’s a detailed comparison table in the third source. It talks about channel formation, threshold voltage, biasing needs, switching behavior, and other traits of depletion and enhancement mode MOSFETs. This table helps readers quickly see how these two MOSFET modes are different.
Depletion mode MOSFETs are “normally on.” This means they let current pass without needing gate voltage. In contrast, enhancement MOSFETs are “normally off.” They need a gate voltage to allow current flow. Depletion and enhancement MOSFETs also differ in their threshold voltages. Depletion mode MOSFETs can have positive or negative threshold voltages. But, enhancement mode ones have a set voltage that must be crossed to turn them on.
The table also talks about how they’re turned off and on, and their switching behavior. With depletion mode, switch off needs a gate voltage of opposite polarity. But for enhancement mode, switching on requires a forward bias gate. This table summarizes all the main points. It helps readers understand the differences quickly, making it easier to learn about these MOSFET types and when to use them.
Source Links
- https://www.circuitbread.com/tutorials/nmos-vs-pmos-and-enhancement-vs-depletion-mode-mosfets
- https://www.electricaltechnology.org/2021/04/difference-depletion-enhancement-mosfet.html
- https://en.wikipedia.org/wiki/Depletion_and_enhancement_modes
- https://www.electronicshub.org/mosfet/
- https://www.aldinc.com/pdf/IntroDepletionModeMOSFET.pdf
- https://www.tutorialspoint.com/difference-between-jfet-and-mosfet
- https://www.rfwireless-world.com/Terminology/Depletion-MOSFET-vs-Enhancement-MOSFET.html