B. S. Passmore

Room Temperature Near-Infrared Photoresponse Based on Interband Transitions in

Near-infrared photoresponse is observed in the temperature range of 77-300 K for a photodetector fabricated from undoped In0.35Ga0.65As/GaAs multiple quantum dots grown in a molecular beam epitaxy system. The detectivity is estimated to be on the order of 3.70 times 109 and 2.70 X 107 cm .radicHz/W at 77 and 300 K, respectively. The reduction of the detectivity is attributed to the increase of the dark current as the temperature is increased. The photoresponse is explained in terms of several interband transitions. These transitions are found to be in good agreement with the self-consistent theoretical calculations.

\hbox{In}_{0.35}\hbox{Ga}_{0.65}\hbox{As}

Two broadband photoresponse from InAs quantum dots embedded in graded InGaAs quantum well photodetectors were observed in the spectral regions of 4–12μm (midinfrared band) and 0.5–1.0μm (near-infrared-visible band). The midinfrared band is attributed to the intersubband transitions within the quantum dots and was observed at temperatures less than 80K. The near-infrared-visible band is attributed to interband transitions and is observed in the temperature range of 77–300K. The room temperature detectivity of the near-infrared-visible band is estimated to be on the order of ∼3.0×108cmHz∕W with a bias voltage less than 1.0V.

Multiple Quantum Dot Photodetector

Optical absorption spectra of intersubband transitions in In0.3Ga0.7As∕GaAs multiple quantum dots were investigated using the optical absorption as a function of the number of In0.3Ga0.7As monolayers deposited using the molecular-beam epitaxy Stranski–Krastanow technique. The peak position energy reached 13.7μm for a sample containing 50 monolayers of In0.3Ga0.7As. The lack of the observation of intersubband transitions in small quantum dots, where the number of the deposited monolayer is less than 15 monolayers, is an indication of the absence of quantum confinement. On the other hand, the presence of high dislocations density in larger quantum dots, where the deposited number of monolayers exceeds 50, could be the reason of why the intersubband transitions are degraded.

Dual broadband photodetector based on interband and intersubband transitions in InAs quantum dots embedded in graded InGaAs quantum wells

Intersubband transitions in GaN∕AlN short period superlattices prepared by molecular beam epitaxy were investigated using the optical absorption technique. The peak position wavelengths of these transitions are found to span the spectral range of 1.35–2.90μm for samples cut into 45° waveguides with GaN quantum well thicknesses ranging between 1.70 and 2.41nm. The Fermi energy levels are estimated from the carrier concentrations, which were measured using an electrochemical capacitance-voltage profiler. The well widths were inferred from comparing the measured peak position energy of the intersubband transitions and the bound state energy levels calculated using the transfer matrix method.

Tuning In0.3Ga0.7As∕GaAs multiple quantum dots for long-wavelength infrared detectors

InAs/GaAs quantum dot infrared photodetectors with different doping levels were investigated to understand the effect of quantum dot filling on both intraband and interband optical transitions. The electron filling of self-assembled InAs quantum dots was varied by direct doping of quantum dots with different concentrations. Photoresponse in the near infrared and middle wavelength infrared spectral region was observed from samples with low quantum dot filling. Although undoped quantum dots were favored for interband transitions with the absence of a second optical excitation in the near infrared region, doped quantum dots were preferred to improve intraband transitions in the middle wavelength infrared region. As a result, partial filling of quantum dot was required, to the extent of maintaining a low dark current, to enhance the dual-band photoresponse through the confined electron states.

Near-infrared wavelength intersubband transitions in GaN/AlN short period superlattices

Over the past two decades, infrared detection has become an important application. There have been many theoretical and experimental studies focused on the intersubband transitions in multiple quantum well systems. We report on the two-color multiple quantum well infrared photodetector. The reported detector consists of two stacks of InGaAs wells and AlGaAs barriers grown on semi-insulating GaAs substrate for mid-wavelength infrared detection. The photoresponse was measured and analyzed on this device, which confirm presence of the intersubband transitions at 6.3 mum and 5.5 mum. In addition, the transfer matrix method is used to estimate the peak position energies of the intersubband transitions in the two stacks. Furthermore, the temperature dependence of photoresponse was measured under a bias voltage of -2.5V. The photoresponse was remained observable at temperature as high as 110K.

The impact of quantum dot filling on dual-band optical transitions via intermediate quantum states

Interband and intersubband transitions in self-assembled InAs quantum dots embedded in an InGaAs graded well have been investigated for their use in visible to mid-infrared (0.4 - 20 μm) detection applications. The materials were grown by molecular beam epitaxy and characterized using atomic force microscopy and photoluminescence. Devices were fabricated from the multiple quantum dot structures in order to measure the normal incident photoresponse at 77 and 300 K. In addition, the dark current was measured in the temperature range of 77 - 300 K for the devices. A dual broadband photoresponse from the interband and intersubband transitions was measured to be 0.5 to 1.0 μm and 2.0 to 14.0 μm, respectively.

Intersubband Transitions in Quantum Wells Infrared Photodetector

The interband and intersubband transitions in self-assembled InAs and In 0.3 Ga 0.7 As quantum dots grown by molecular beam epitaxy have been investigated for their use in visible, near-, and mid-infrared detection applications. Devices based on InAs quantum dots embedded in an In x Ga 1−x As (0 to 0.3) graded well and In 0.3 Ga 0.7 As quantum dots were fabricated in order to measure the temperature dependent (77 – 300 K) photoresponse. The dark current was measured in the temperature range of 77 to 300 K for the devices. Room temperature photoresponse ranging between 0.6 to 1.3 μm was observed for the InAs and In 0.3 Ga 0.7 As quantum dot photodetectors. Furthermore, a dual band photoresponse in the visible, near-, and mid-infrared spectral regions for both devices was observed at 77 K. Using a self-consistent solution of Schrodinger-Poisson equations, the peak position energies of the interband and intersubband transitions in the two multi-color quantum dot infrared photodetector structures was calculated.

Broadband photoresponse from InAs quantum dots embedded in a graded well for visible to mid-infrared detection

A voltage-tunable two-color multiple quantum well infrared photodetector was fabricated with two bands at 6.0 and 10.3 im. The molecular beam epitaxy grown structure consists of two stacks of n-type InGaAs wells and GaAs/AlGaAs superlattice barriers. The 6.0 im band was found to be dominant at low bias voltages while the 10.3 im band is dominant at high bias voltages. The optical absorption measurements confirm the presence of both bands. Furthermore, the transfer matrix method is used to estimate the peak position energies of the intersubband transitions in the two stacks.

Multi-color Photoresponse Based on Interband and Intersubband Transitions in InAs and InGaAs Quantum Dot Photodetectors

The optical absorption spectra of intersubband transitions in In 0.3 Ga 0.7 As/GaAs multiple quantum dots (MQDs) grown by molecular beam epitaxy were investigated. By varying the number of In 0.3 Ga 0.7 As monolayers deposited, a series of samples with varying dot sizes ranging from 10 – 50 monolayers were obtained. The quantum dots grown with size less than 15 monolayers or more than 50 monolayers did not yield any observable measurements of intersubband transition. This suggests that there exist a critical upper and lower limit of In 0.3 Ga 0.7 As quantum dots for infrared detectors. A wavelength range of 8.60 – 13.70 μm is achieved for structures grown with the above monolayers range. The theoretical line-shape of the intersubband transition absorption was compared to the experimental measurements. From the lineshape, it was deduced that bound-to-continuum transtition is present in thick quantum dots and bound-to-bound transition is present in thinly grown quantum dots.