Semiconductor device having reduced contact resistance between a channel or base layer and a contact layer

A semiconductor device comprising:

• a first p-type semiconductor layer;
• a second undoped or donor impurity doped semiconductor layer formed in contact with one side of said first semiconductor layer;
• a third undoped or donor impurity doped semiconductor layer formed on a side of said second semiconductor layer opposite to said first semiconductor layer;
• and
• a fourth p-type semiconductor layer which is a separate body from said first semiconductor layer;
• wherein said first semiconductor layer and said second semiconductor layer are equal in a sum of electron affinity and band gap, said third semiconductor layer is smaller in the sum of electron affinity and band gap than said second semiconductor layer, said second semiconductor layer acts as a carrier bypass path forming layer, and said first or second semiconductor layer is in direct contact with said fourth semiconductor layer.

A semiconductor device comprising:

• a first n-type InGaAs layer;
• a second undoped or acceptor impurity doped InGaAs layer formed in contact with one side of said first InGaAs layer;
• an undoped or acceptor impurity doped GaAs layer formed on a side of said second InGaAs layer opposite to said first InGaAs layer;
• and
• an n-type semiconductor layer which is a separate body from said first InGaAs layer;
• wherein said second InGaAs layer acts as a carrier bypass path forming layer, and said separate n-type semiconductor layer is formed in contact with said first second InGaAs layers.

A semiconductor device comprising:

• a first p-type InGaAs layer;
• a second undoped or donor impurity doped InGaAs layer formed in contact with one side of said first InGaAs layer;
• an undoped or donor impurity doped GaAs layer formed on aside of said second InGaAs layer opposite to said first InGaAs layer;
• and
• and a p-type semiconductor layer which is separate body from said first InGaAs layer;
• wherein said second InGaAs layer acts as a carrier bypass path forming layer, and said separated p-type semiconductor layer is formed in contact with said first and second InGaAs layers.