C. R. H. White

Electroluminescence and impact ionization phenomena in a double‐barrier resonant tunneling structure

Electroluminescence (EL) due to impact ionization in the high field region of a double‐barrier resonant tunneling structure is reported. Knowledge of the charge distribution in the structure enables a detailed analysis to be made of the impact ionization rate as a function of electric field. Large peak‐to‐valley ratios of 15:1 in the EL emission intensity from the quantum well active region are observed.

Resonant magnetotunnelling of electrons and holes in a p-i-n diode device incorporating a double barrier structure

The authors observe resonant tunnelling of electrons and holes in a GaAs p-i-n diode incorporating two AlAs barriers in the undoped region. Peaks due to the HH1, LH1, E1 and HH2 (E=electron, LH=light hole, HH=heavy hole) resonances are observed, in that order of increasing voltage. The voltage separation of the LH1 and E1 resonance is significantly larger than expected from a simple quantum mechanical model due to an interaction effect involving resonant buildup of electron space charge in the quantum well. High magnetic fields B//J and B perpendicular to J are used to investigate the device and confirm the assignment of the resonances.

A direct comparison of the quantized Hall resistance in high critical current gallium arsenide and silicon devices

By use of an ultra-sensitive cryogenic current comparator bridge the quantized Hall resistance RH(i) for i = 2 in a GaAs/AlGaAs heterostructure has been compared directly with RH(4) in a silicon MOSFET. We find RH(2; GaAs)/RH(4: Si) = 2(1 − 0.22(3.5) × 10−10) demonstrating that within the 1σ combined uncertainty of ± 3.5 × 10−10 the quantized Hall resistance is independent of the host lattice and Landau level index, and probably equal to he2. This accuracy is such that corrections to RK of order (lB/ohms)2, where lB is the magnetic length and ohms the specimen width, can almost be discounted. The extremely high c current achieved in the MOSFET structures (∼ 70 microA) seems to be simply due to the particularly thick (800 nm) oxide layers used. GaAs quantum well devices are found to be well suited to metrology work. Devices with mobilities of ∼ 20 m2 V −1s −1 show the highest critical currents while the suitable scaled plateaux widths are only weakly dependent upon mobility.

Magnetic field investigations of n−(AlIn)As(InGa)As resonant tunnelling devices grown by MOCVD

Abstract MOCVD- grown double barrier structures based on n − (AlIn)As (InGa)As are investigated. Resonant tunnelling into two bound states of the well is observed, with peak-to-valley ratios of 2.1:1 on the lower resonance at room temperature (15.3:1 at 77 K). Magnetoquantum oscillations in the tunnel current for B z.sfnc;z.sfnc; J provide evidence for two two-dimensional subbands in the emitter accumulation layer, for charge build-up in the well at resonance and for scattering of electrons between the two bound states of the well by LO phonon emission.

The observation of the fractional quantum Hall effect in a single (AlGa)As/GaAs/(AlGa)As quantum well

The fractional quantum Hall effect (FQHE) is observed at filling factors of nu =2/3, 4/3 and 5/3 for conduction electrons confined in a single (AlGa)As/GaAs/(AlGa)As quantum well of thickness 102 AA. The variation of mobility with carrier concentration following below band-gap illumination is also measured.

Quantum well luminescence due to minority photoelectrons in p-type resonant tunnelling structures

Photoluminescence spectroscopy is used to investigate p-type double-barrier resonant tunnelling structures based on GaAs/AlAs. Strong photoluminescence from the quantum well is observed due to recombination of resonantly tunnelling holes with minority photogenerated electrons, which also tunnel into the quantum well. The luminescence undergoes a red shift with increasing bias and its intensity shows peaks at biases corresponding to the first four hole resonances in the current-voltage characteristics. Two additional strong peaks are also seen in this intensity-bias plot, due to electron resonant tunnelling.

Optical Spectroscopy of Double Barrier Resonant Tunneling Structures

Recent applications of optical spectroscopy to the study of double barrier resonant tunneling structures are discussed. Particular topics emphasized are the determination of charge build up in the quantum well active region on resonance, determination of the nature of the tunneling processes and the detection of electroluminescence emission resulting from impact ionisation in double barrier structures.

Quantum Well Luminescence by Resonant Tunneling Injection of Electrons and Holes

The electroluminescence and current-voltage characteristics of two forward biased p-i-n double barrier structures based on GaAs/AlAs are investigated. Electroluminescence lines due to carrier recombination in the GaAs contact layers and in the quantum well are observed. The bias dependence of the intensity of these lines exhibits pronounced peaks which are also seen in the I(V) characteristics and which are due to electron and hole resonant tunneling into the quantum well. Two quantum well emission lines are observed in the electroluminescence spectrum. Their relative intensity is strongly dependent on the concentration of electrons in the quantum well, which can be varied by a large amount by voltage tuning on and off the electron resonance. Photoluminescence excitation spectroscopy measurements indicate that the two quantum well emission lines involve recombination of electrons with holes in the lowest heavy hole state (HH1) and holes bound to acceptors in the quantum well.

Intrinsic bistability in the current-voltage characteristics and electroluminescent emission of resonant tunnelling structures

Abstract Intrinsic bistability in the current-voltage characteristics of double-barrier semiconductor heterostructures arises from the electrostatic effect of the electronic space charge which builds up in the quantum well at resonance. We describe how the effect of a quantising magnetic field greatly enhances this process due to the singularities in the density of electronic states associated with Landau level formation. Appropriately-designed n-type resonant tunneling devices spontaneously emit light (electroluminescence) due to the formation of minority carriers (holes) in impact ionisation processes. The electroluminescence emission can also exhibit a marked intrinsic bistability. We present a microscopic description of the origin of this “optoelectronic memory” effect.

Investigation of a double barrier resonant tunnelling structure which incorporates an optical window layer in the top contact

Abstract The electrical and optical properties of a double barrier resonant tunnelling device based on n-GaAs/(AlGa)As and incorporating a heavily doped (AlGa)As window layer are described. The window layer is located between the quantum well and the top surface and has a band gap which exceeds the energy of the quantum well photoluminescence. The incorporation of this layer does not impair the electrical properties of the device.