Andreas Marent

The QD-Flash: a quantum dot-based memory device

We demonstrate the large potential of III?V compound semiconductors for a novel type of Flash memory. The concept is based on self-organized III?V quantum dots (QDs). Here the advantages of the most important semiconductor memories, the dynamic random access memory and the Flash are merged. A non-volatile memory with fast access times ( 1015 write/erase cycles) as an ultimate solution seems possible. A storage time of 1.6 s at 300 K in InAs/GaAs QDs with an additional Al0.9Ga0.1As barrier was demonstrated and a retention time of 106 years is predicted by us for GaSb QDs in an AlAs matrix. In addition, a minimum write time of 6 ns is obtained for InAs/GaAs QDs. First prototypes with all-electrical data access prove the feasibility of the concept. The stored information is read-out by a two-dimensional hole gas underneath the QD layer. Time-resolved drain-current measurements demonstrate the memory operations.

A novel nonvolatile memory based on self-organized quantum dots

A novel type of memory based on self-organized quantum dots (QDs) is presented, which merges the advantages of the most important semiconductor memories, the dynamic random access memory (DRAM) and the Flash. A nonvolatile memory with fast access times ( 1015 write/erase cycles) as an ultimate solution seems possible. A storage time of 1.6s at 300K in InAs/GaAs QDs with an additional Al0.9Ga0.1As barrier is demonstrated and a retention time of 106 years is predicted for GaSb QDs in an AlAs matrix. A minimum write time of 6ns is obtained for InAs/GaAs QDs. This value is already in the order of the access time of a DRAM cell and at the moment limited by the RC low pass of the device. An erase time of milliseconds is shown in first measurements on GaSb/GaAs QDs at 100K. Faster write/erase times below 1ns even at room temperature are expected for improved device structures.

Antimony-based quantum dot memories

As a type-II heterostructure with exclusive hole confinement GaSb/(Al,Ga)As QDs are an ideal candidate for a QD based memory device operating at room temperature. We investigated different Antimony-based QDs in respect of localization energies and storage times with 8-band-k•p calculations as well as time-resolved capacitance spectroscopy. In addition, we present a memory concept based on self-organized quantum dots (QDs) which could fuse the advantages of todays main semiconductor memories DRAM and Flash. First results on the performance of such a memory cell are shown and a closer look at Sb-based QDs as a storage unit is taken.

Self-organized quantum dots for future semiconductor memories

A memory structure based on self-organized quantum dots (QDs) combining the advantages of dynamic random access memory (DRAM) and flash memory which enables extremely fast write times (<1 ns) together with long storage times ( years) at room temperature is presented. A storage time of 1.6 s at 300 K in InAs/GaAs QDs with an additional Al0.9Ga0.1As barrier—100 times longer than in a DRAM—is demonstrated. Much longer retention times of 106 years are predicted for GaSb QDs in an AlAs matrix. A minimum write time of 6 ns is currently obtained for InAs/GaAs QDs, of the order of those for present DRAMs. An even faster write time below 1 ns, only limited by charge carrier capture and relaxation times (in the order of picoseconds), is predicted for a slightly improved device structure.

Direct observation of charge-carrier capture in an array of self-assembled InAs/GaAs quantum dots

In this work, charge-carrier capture by an array of self-assembled InAs/GaAs quantum dots was directly observed for the first time by capacitance recharge. It is proposed to process the obtained transient-capture data by a similar method to that used for emission, by the box-car method. The capture activation energies are determined and compared with the emission activation energies.