GaAlAs/GaAs floating-gate memory devices with graded-gap injector grown by molecular-beam epitaxy

The operation of the first floating-gate memory device in the AlGaAs/GaAs material system is reported. The devices were grown by molecular-beam epitaxy and consist of an undoped GaAs floating gate 2000 Å thick separated from the 750-Å n≈1×10 ¹⁷ GaAs channel by an undoped 1000-Å AlAs barrier. On the other side of the floating gate an undoped 200-Å AlAs barrier was grown, followed by an 1800-Å compositionally graded injector. Measurements were performed from room temperature down to liquid-nitrogen temperature by monitoring the channel conductance at fixed source-to-drain bias. The measurements indicate, for the electron escape from the floating gate, an activation energy of ≈0.2 eV, which is consistent with the measured GaAs-AlAs conduction-band discontinuity. The memory device is erased either optically or by applying a positive pulse on the gate. The experimental storage times look promising in applications such as dynamic random-access memories and permanent memories, depending on the temperature of operation