Quantum dot infrared photodetector (QDIP) and methods of making the same

Abstract

A photodetector capable of normal incidence detection over a broad range of long wavelength light signals to efficiently convert infrared light into electrical signals. It is capable of converting long wavelength light signals into electrical signals with direct normal incidence sensitivity without the assistance of light coupling devices or schemes. In the apparatus, stored charged carriers are ejected by photons from quantum dots, then flow over the other barrier and quantum dot layers with the help of an electric field produced with a voltage applied to the device, producing a detectable photovoltage and photocurrent. The photodetector has multiple layers of materials including at least one quantum dot layer between an emitter layer and a collector layer, with a barrier layer between the quantum dot layer and the emitter layer, and another barrier layer between the quantum dot layer and the collector.

We claim:  
     
         1 . A method of producing self-assembled quantum dots having an adjustable number of confined levels and having an adjustable intersublevel spacing which relies on spontaneous island formation during the epitaxy of highly strained semiconductors comprising: 
 selecting a barrier material and a quantum dot material wherein the amount of their lattice-mismatch dictates a critical thickness required to obtain the spontaneous island formation, and their bandgap difference determines a possible number of confined states in conjunction with the intersublevel spacing;    growing some thickness of the barrier material which has a lattice constant close to the lattice constant of the substrate used;    depositing, at a specified growth rate, the quantum dot material at a substrate temperature which will produce quantum dots having an appropriate size to obtain the intersublevel spacing;    stopping the growth of the quantum dot material after a desired number of quantum dots per unit area is reached;    pausing the growth of the quantum dot material for a predetermined amount of time to allow for self-assembling growth to form the quantum dots in shapes and sizes which will give the intersublevel spacing; and    growing a thickness of the barrier material to cover the quantum dots and return to a planar growth front at a substrate temperature which may be varied during the growth and which will optimize the quality of the quantum dots.    
     
     
         2 . The method of claim  15  wherein the intersublevel spacing is between 5 meV and 150 meV, the number of confined states is between 1 and 20, the substrate is GaAs, the barrier material is Al x1 Ga 1−x1 As and the quantum dots are comprised of Al x4(1−x3) Ga (1−x4)(1−X3) In x3 As.