Double heterojunction semiconductor device with injector

A semiconductor device comprising:

• (a) a first semiconductor layer having a low carrier density, a first election affinity, and a first energy band gap,
• (b) a second semiconductor layer formed on said first semiconductor layer and having a low carrier density, a second election affinity, and a second energy band gap, a sum of said second electron affinity and said second energy band gap being smaller than a sum of said first electron affinity and said first energy band gap, a heterojunction being formed between the first and second semiconductor layers,
• (c) a third semiconductor layer formed on said second semiconductor layer and having a third electron affinity smaller than said second electron affinity, a heterojunction being formed between said second and third semiconductor layers,
• (d) a fourth semiconductor layer formed on said third semiconductor layer for injecting carriers of one type into said second semiconductor layer through said third semiconductor layer for inducing a channel of carriers of another type in said second semiconductor layer in proximity to and along an interface between the second and third semiconductor layers,
• (e) a pair of ohmic contact regions extending through said second and third semiconductor layers into said first semiconductor layer for providing ohmic contact at least with said second semiconductor layers,
• (f) a control electrode, provided on said fourth semiconductor layer, for injecting said carriers of said one type into said second semiconductor layer through said fourth semiconductor layer, and
• (g) means for producing a voltage between said control electrode and at least one of said ohmic contact regions, said carriers of said one type being injected in response to said voltage, wherein conductance between the ohmic contact regions in response to injection of said carriers of said one type from said fourth semiconductor layer into said second semiconductor layer is modulated.