Threshold extension of gallium arsenide/aluminum(x) gallium(1-x) arsenide terahertz detectors and switching in heterostructures.

摘要

In this work, homojunction interfacial workfunction internal photoemission (HIWIP) detectors based on GaAs, and heterojunction interfacial workfunction internal photoemission (HEIWIP) detectors based mainly on the GaAs/Al xGa1-xAs material system are presented. Design principles of HIWIP and HEIWIP detectors, such as free carrier absorption, photocarrier generation, photoemission, and responsivity, are discussed in detail. Results of p-type HIWIPs based on GaAs material are presented. Homojunction detectors based on p-type GaAs were found to limit their operating wavelength range. This is mainly due to band depletion arising through carrier transitions from the heavy/light hole bands to the split off band. Designing n-type GaAs HIWIP detectors is difficult as it is strenuous to control their workfunction.;Heterojunction detectors based on GaAs/AlxGa 1-xAs material system will allow tuning their threshold wavelength by adjusting the alloy composition of the Al xGa1-xAs barrier, while keeping a fixed doping density in the emitter. The detectors covered in this work operate from 1 to 128 microm (300 to 2.3 THz). Enhancement of detector response using resonance cavity architecture is demonstrated. Threshold wavelength extension of HEIWIPs by varying the Al composition of the barrier was investigated. The threshold limit of ∼ 3.3 THz (92 microm), due to a practical Al fraction limit of ∼ 0.005, can be overcome by replacing GaAs emitters in GaAs/AlxGa1-xAs HEIWIPs with AlxGa1-xAs emitters. As the initial step, terahertz absorption for 1 microm-thick Be-doped AlxGa1-xAs epilayers (with different Al fraction and doping density) grown on GaAs substrates was measured. The absorption probability of the epilayers was derived from these absorption measurements. Based on the terahertz absorption results, an AlxGa1-xAs/GaAs HEIWIP detector was designed and the extension of threshold frequency ( f0) to 2.3 THz was successfully demonstrated.;In a different study, switching in GaAs/AlxGa1- xAs heterostructures from a tunneling dominated low conductance branch to a thermal emission dominated high conductance branch was investigated. This bistability leads to neuron-like voltage pulses observed in some heterostructure devices. The bias field that initiates the switching was determined from an iterative method that uses feedback information, such as carrier drift velocity and electron temperature, from hot carrier transport. The bias voltage needed to switch the device was found to decrease with the increasing device temperature.