Self Assembled Quantum Dot Devices

Quantum Dot Infrared Photodetectors (QDIPs)

Researchers at the Center for Quantum Devices have demonstrated the self-assembled growth of In(Ga)As quantum dots in both InP-based and GaAs based systems using metalorganic chemical vapor deposition. The quantum dots are grown by self-assembly under the Stranski-Krastanow growth mode. The dots can be visualized using atomic force microscopy.

AFM micrographs of: a 1 μm x 1 μm surface imaging of InAs quantum dots on GaAs/InP, (inset) a single InAs quantum dot.

Using such dots, we have demonstrated a multi-stack quantum dot infrared photodetector (QDIP). Such QDIPs have many advantages compared to the conventional quantum well infrared photodetector (QWIP), including: higher responsivity, higher temperature operation, higher light coupling to normal incidence light, and capability of narrow band te nability. A variety of QDIP and quantum dot-quantum well hybrid devices have been grown on both GaAs and InP substrates.

 

Illustration (left) and typical SEM imaging (right) of the cross section of a QDIP

QDIPs on GaAs

In the InGaAs/InGaP/GaAs QDIP devices, the spectral response exhibited an intersubband transition at 4.7 μm at 77 K. The peak responsivity was measured as a function of temperature up to 200 K. The record high detectivity was 1.1x1012 cm·Hz½/W at 77 K and 5.5x1010 cm·Hz½/W at 120 K. BLIP operation was achieved up to 180 K.

Image of a soldering iron from a focal plane array based on InGaAs/InGaP/ GaAs MWIR QDIP.

In addition, the world's first QDIP focal plane array (FPA) was also demonstrated, based on the InGaAs/InGaP/GaAs QDIP with a 256x256 format. The image could be seen at temperatures as high as 120 K and NEΔT was about 509 mK at 77 K.

Thermal imaging of the human body taken by our 256 x 256 InGaAs/GaAs/ InGaP DWELL FPA. Note the clear blood vessels on the hands.

We have also demonstrated a LWIR GaAs-based QDIP operating at 9 μm at 77K. This device utilizes a InGaAs/GaAs Dot-in-a-Well structure (DWELL) with In- GaP barriers. A 256x256 FPA was also demonstrated operating at 68 K.

QDIPs on InP

Image of a soldering iron from a focal plane array based on InAs/InP MWIR QDIP.

The world's first InP based QDIPs were demonstrated at the Center for Quantum Devices using InAs QDs. The peak detection wavelength was 6.4 μm at 80K with peak responsivity of 843 mA/W at -5 V bias, with a peak detectivity of 1 x 1010 cm·Hz½/ W at -1.1 V bias. Additionally, a 256x256 focal plane array based on the InAs/InP QDIP was also demonstrated.

 

 Thermal imaging of a soldering iron taken by our 320x256 InAs/InGaAs/InAlAs/InP MWIR QDIP FPA operating at 200 K, left. Thermal imaging of the human body taken by our 320x256 InAs/InGaAs/InAlAs/InP MWIR QDIP FPA operating at 130K, right.

QDIP devices operating at room temperature with high quantum efficiency were demonstrated using an InAs QD / InGaAs QW hybrid device with InAlAs barriers. The peak detection wavelength was 4 μm. At 150 K the detectivity was 1 x 1011  cm·Hz½/ W and the internal quantum efficiency was 67 %. A 320 x 256 FPA based on the same structure was fabricated and operated at temperatures up to 200K. 

 

Other QDIPs

Similar QDIP structures were also grown on silicon substrates for the first time ever reported. The low temperature spectral response revealed a peak response of 5.91 μm at 16 K.

Quantum Dot Lasers

Based on the same quantum dot growth technique as for QDIP, researchers at the Center for Quantum Devices have demonstrated a quantum dot laser diode.

The multidimensional quantum confinement of quantum dot laser was predicted to exhibit extremely low threshold currents, higher modulation bandwidth, narrower spectral linewidth, and reduced temperature sensitivity compared with their quantum well laser structure counterparts.

 

Schematic of a QD laser structure, left. P-I characteristics and emission spectrum of a quantum dot laser diode. right.

The diode structure is schematically shown in the figure above. Stimulated emission was observed at 995 nm with an injection current of 400 mA.

Last Updated 10/08/2008

Northwestern University