Two-dimensional electron gas sensor and methods for making and using the sensor

A method for making a sensor for sensing the presence of at least one fluidum in a space adjoining the sensor, comprising a two-dimensional electron gas (2DEG) layer stack, a gate lying adjacent to at least part of the 2DEG layer stack for electrostatically controlling electron density of a 2DEG in the 2DEG layer stack and a source electrode contacting the 2DEG layer stack for electrically contacting the 2DEG, the method comprising:

• providing a nucleation layer on a substrate;
• and
• growing the 2DEG layer stack on the nucleation layer,
• wherein growing the 2DEG layer includes, during growth, diffusing atoms of the nucleation layer into the substrate to form a doped semiconductor bottom layer of the 2DEG layer stack,
• wherein a gate electrode is provided in electrical contact with the doped semiconductor bottom layer, and
• wherein the doped semiconductor bottom layer forms the gate.

A sensor, comprising:

• a substrate;
• a two-dimensional electron gas layer stack, comprising:
• a first semiconductor layer formed over the substrate, the first semiconductor having a first band gap, and
• a second semiconductor layer formed on the first semiconductor layer, the second semiconductor layer having a second band gap wider than the first band gap,
• wherein a heterojunction is formed at a junction formed between the first and second semiconductor layers;
• a conductive back gate formed between the substrate and the first layer, wherein the heterojunction forms a two-dimensional electron gas conduction layer in response to a voltage applied to the conductive back gate;
• and
• a contact surface formed on a surface of the second semiconductor, wherein the contact surface is configured to be in contact with a fluidum and to change the conductivity of the two-dimensional electron gas conduction layer in response to the molecules of the fluidum contacting the contact surface.