Aluminium Gallium Nitride (AlGaN) Semiconductors

Topics Covered

Description
Applications
Chemical Properties
Electrical Properties
Thermal Optical Properties
Recent Developments

Description

Aluminium gallium nitride is an alloy of aluminium nitride and gallium nitride with useful semiconductor properties. When grown on GaN, it gives rise to fixed charges at the interface stemming from piezoelectric effects. These charges in turn induce the presence of free carriers called two dimension electron gas whose flow can be controlled by the gate of the transistor.

It is the most studied semiconductor for GaN microelectronics.

Applications

Aluminum gallium nitride finds applications in the following:

  • Detectors of ultraviolet radiation
  • Semiconductor lasers
  • AlGaN/GaN high electron mobility transistor (HEMT) transistors.

Chemical Properties

The chemical properties of aluminum gallium nitride are provided in the table below:

Chemical Properties
Chemical Formula AlGaN
Group Aluminum – 13
Gallium – 13
Nitrogen - 15
Lattice Constant 3.17 Å

Electrical Properties

The electrical properties of aluminum gallium nitride are provided in the table below:

Electrical Properties
Electrical Resistivity 2.5 Ω mm
Band Gap 4.3 – 6.2 eV
Electron Mobility (@ x=0.25) 900 - 2000 cm2/Vs

Thermal Optical Properties

The thermal properties of aluminum gallium nitride are provided in the tables below:

Thermal Properties
Thermal Conductivity 1.3 – 2.1 W/cmK

Recent Developments

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Coffie, R et al (2004) demonstrated a high-power GaN/AlGaN/GaN HEMT (high-electron-mobility transistor). It employs a thick cap layer to cover screen surface states and minimize dispersion, and a deep gate recess to achieve the desired transconductance. In addition, a thin SiO2 layer was deposited on the drain side of the gate recess to regulate gate leakage current and improve breakdown voltage.

No surface passivation layer was used, and a breakdown voltage of 90 V was achieved. A record output power density of 12 W/mm with an associated power-added efficiency of 40.5% was measured at 10 GHz. The results showed that HEMT has the potential to decrease dispersion and produce power without surface passivation.

Vetury, R et al (2008) presented wear out reliability assessment of AlGaN HEMTs fabricated on SiC based on three temperature 48 V dc stress tests. They also compared the impact of dc and RF stress and conducted additional experiments on a smaller sample set. The results indicated that the impact of dc and RF stress is not significantly different.

Soltani A et al (2009) analyzed the ohmic contact formation on AlGaN/GaN, AlGaN/AlN/GaN and GaN HEMT. TEM measurement was carried out on these devices to understand the ohmic contact formation for Ti and Ti/Al contact. The ohmic behavior of these structures was analyzed rapidly and easily by etching the AlGaN barrier.

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