Research On Quantum Dots-In-Well Photodevice Characteristic And Singnal Readout

As the gain or absorption medium for optoelectronic devices,some key scientific problems of quantum dots(QDs)need to be further studied.Apart from the zero-dimensional quantum size effect,quantum dots can also show the characteristics of low threshold current density and low noise when used in lasers and detectors,so they have high practical value.The quantum dot-in-well devices can be used as light detector,also can be used as optical storage device(hereinafter generally referred to quantum dot-in-well photodevice),which it can get low dark current,high detection rate and the wavelength tunable characteristics based on the carrier with long life.However,there are still some problems to solve,such as the tradeoff between high gain and response speed,the relationship between quantum dot detection and storage,and so on.The article focuses on researching the response speed of the quantum dot in-well photodevice,the storage time,the weak signal detection capability etc,and research infrared photoelectric device readout at low temperature as well as the readout signal processing.The main research contents of the thesis are as follows:1.The transient response characteristics of the quantum dots-in-well photodevice(the device sample was developed by Semiconductor Research Institute of Chinese Academy of Sciences(CAS),the same below,unless otherwise specified)under laser irradiation with a wavelength of about 800 nm were studied.When the light pulse width was 100 ps,the transient response time of the device at room temperature was 5.2ns.In addition,the non-linear equations of devices under different operating modes are studied,and the equivalent circuits of quantum dot detectors are established by genetic algorithm.The non-linear problems are transformed into global optimal solutions,and the equivalent circuit models under different light intensities are extracted.2.On the basis of the test from semiconductor institute of CAS and their research on the electron and hole separated in the space and stored in quantum well and quantum dot respectively at a certain bias,the "step current" I-V curve and the "fish eye" C-V curve behavior of the quantum dots-in-well photodevice have been investigated.The holes are stored in the QDs and deleted by bias.The storage time is at the order of milliseconds proved by pulsed photovoltage/photocurrent response ratio of the photodevice.The storage time is about 0.6 s.The test shows that the size of the storage window is related to the device bias,and the storage time is independent of the bias voltage.3.The photodevice sample of semiconductor institute of CAS has been analyzed by the PL spectra.The sample B of high gain and sample A with storage characteristics have the same peak strength.The difference is the energy level of quantum well and defect energy level.The sample B has a higher well energy level and the same bias or light intensity makes the hole in quantum dot more prone to overflow,and it shows higher sensitivity.The storage time noticed for the sample A has the higher sensitivity when the lower light(nW)level,and on storage when light stronger.From the CV curve tested of the sample A,its electron hole pairs are generated to recombination at weak light,while the storage charge is very small.Under the stronger light,the storage charge increases with the increase of light quantity.4.In order to meet the requirements of the infrared imaging system with high sensitivity and high resolution,the readout circuit often has been placed at low temperature to reduce thermal noise and suppress dark current.Based on the readout circuit of the team,the W/L ratio of CMOS unit device is adjustused by simulating low-temperature.The working state of the MOS device and readout circuit have been studied from 20 to 300 K to design the deep low temperature readout circuit.After 0.35 ?m 2P4 M digital-analog mixed circuit process and ceramic substrate packaging,it has been preliminary proved by test that the operating temperature of the circuit was close to 40 K.5.In infrared readout system,the stability of bias voltage of readout circuits is an important which impact on the whole system,and even directly affects the final readout signal.A bandgap voltage reference with low power consumption,wide temperature range and high PSRR(Power Supply Rejection Ratio)has been designed.The fixed output voltage is 1.21 V,the work temperature range-100 ~ 125?,the PSRR-69 dB,the amplifier gain 82 dB,the overall drive current 400 ?A,the power consumption 5 ?W.In order to increase the dynamic range and realize adaptive integrated capacitance readout,the intelligent readout design has been studied.