Compound semiconductor device, method for manufacturing the same and amplifier

A method for manufacturing a compound semiconductor device, the method comprising:

• preparing a semiconductor laminate structure including an electron transit layer and an electron supply layer that are formed from a compound semiconductor;
• forming a source electrode and a drain electrode above the electron supply layer;
• forming an insulating layer between the source electrode and the drain electrode and over the semiconductor laminate structure;
• forming a gate recess in the insulating layer;
• and
• forming a gate electrode including a first portion in the gate recess and a second portion coupled to the first portion and provided over the insulating layer at a position further on the drain electrode side than the gate recess,
• wherein the forming of the insulating layer includes:
• forming an aluminum oxide film in direct contact with the semiconductor laminate structure;
• and
• subjecting the aluminum oxide film to heat treatment in an oxidizing atmosphere such that a value of x is larger than 1.5 when a composition of the aluminum oxide film is expressed as AlOx and
• wherein the aluminum oxide film is at least located between the second portion and the semiconductor laminate structure in a thickness direction of the insulating layer.

An amplifier comprising:

• a digital predistortion circuit configured to compensate nonlinear distortion of an input signa;
• a mixer configured to mix the input signal from the digital predistortion circuit with an alternate current signal;
• and
• a power amplifier including a compound semiconductor device and configured to amplify the input signal from the mixer,
• wherein the compound semiconductor device includes:
• a semiconductor laminate structure including an electron transit layer and an electron supply layer that are formed from a compound semiconductor;
• a gate electrode, a source electrode, and a drain electrode that are provided above the electron supply layer;
• and
• an insulating layer that is provided between the source electrode and the drain electrode, over the semiconductor laminate structure, and with a gate recess formed therein,
• wherein the gate electrode includes:
• a first portion in the gate recess;
• and
• a second portion that is coupled to the first portion and is provided over the insulating layer at a position further on the drain electrode side than the gate recess,
• wherein the insulating layer includes an aluminum oxide film in direct contact with the semiconductor laminate structure,
• wherein the aluminum oxide film is at least located between the second portion and the semiconductor laminate structure in a thickness direction of the insulating layer, and
• wherein, when a composition of the aluminum oxide film is expressed as AlOx, a value of x is larger than 1.5.