Real-space Transfer Of Hot Electrons Research Articles

Observation of resonant tunneling effects in a three-terminal device

We present the results of studying the resonant tunneling into a single quantum well (SQW) in a three-terminal device. The resonant process manifests itself as a peak and negative-resistance effect in lateral current in the SQW, the amplitude and position of the peak being controlled by the third collector, electrode. In addition, a peak of resonant current with a pronounced negative transconductance was simultaneously measured in the collector circuit as a result of real-space hot-electron transfer from the SQW to the collector.

Negative-resistance field-effect transistor grown by organometallic chemical vapor deposition

Results of studying the process of real space hot electron transfer in the Negative-Resistance Field-Effect Transistor (NERFET) grown by organometallic chemical vapor deposition (OMCVD) are presented. In the modified AlGaAs/GaAs heterostructure we obtain a significant reduction in the parasitic leakage and a drastic improvement of negative differential resistance (NDR) in the drain circuit—with the peak-to-valley current ratio as high as 160 at room temperature. The effect of NDR is proved to be due to real-space transfer of hot electrons from the high mobility channel into the second conducting layer, with the current of transferred electrons depending exponentially on the second conducting layer potential. Analysis shows that the same device can operate as a Charge-Injection Transistor with an available power gain of about 5.

Photoluminescence from GaAs quantum wells under high electric fields

The room-temperature photoluminescence spectra of n-modulation doped GaAs–AlGaAs multiple quantum wells have been studied at high parallel electric fields in order to obtain the distribution function of the two-dimensional electron system under high field conditions. The spectra show thermalized energy distributions with electron temperatures of ∼600 K in the range where current instabilities indicate negative differential conductivity. This temperature is well below the value expected for bulk GaAs, and can be understood on the basis of real-space transfer of hot electrons into AlGaAs.

High-frequency amplification and generation in charge injection devices

Room-temperature high-frequency measurements on a three-terminal amplifying device based on real-space hot-electron transfer between two conducting layers separated by a potential barrier have been performed. The devices grown by organometallic chemical vapor deposition utilize a novel undoped GaAs/AlGaAs heterostructure which, through its dramatically reduced parasitic leakage compared to previous structures, permits, for the first time, operation as a charge injection transistor. The charge injection transistor exhibits true three-terminal amplification due to real-space hot-electron transfer controlled by electron temperature in a high mobility channel. The device demonstrates power and current gains with cut-off frequencies of 9.8 and 29 GHz, respectively, with maximum current gain of 39 dB. In the negative resistance transistor mode, the same device was found capable of microwave generation up to 7.7 GHz. The frequency response of our device is shown to be limited by RC in the output circuit and methods for improvement of the cut-off frequency are discussed.

Switching in NERFET circuits

NERFET is a three-terminal device possessing a pronounced negative differential resistance due to the effect of real-space hot-electron transfer. The device structure, substantially modified compared to our earlier reports, gives an improved performance at room temperature. In this work, logic operation of a circuit formed by two NERFET's is demonstrated for the first time. Sharp switching of output voltage is observed. Using this circuit, we have demonstrated the operation of an inverter and a bistable switch. Under certain bias configurations the circuit also exhibits a tristable behavior which can be used for ternary logic.

Hot-electron memory effect in double-layered heterostructures

We studied a memory effect due to the real-space hot-electron transfer between two conducting GaAs layers separated by a graded AlGaAs barrier. Application of a lateral electric field to one of the layers enhances its electron temperature and leads to a charge injection into the other layer which is kept floating. As the heating voltage is removed, the injected electrons remain in the second layer, giving rise (at low temperatures, 77 K) to a persistent potential difference. Kinetics of the charge-up process are studied at different heating voltages.

Charge injection transistor based on real-space hot-electron transfer

We describe a new transistor based on hot-electron transfer between two conducting layers separated by a potential barrier. The mechanism of its operation consists of controlling charge injection over the barrier by modulating the electron temperature in one of the layers. This physical principle is different from those employed in all previous three-terminal amplifying devices-which are based either on the modulation of a potential barrier (vacuum triode, bipolar transistor, various analog transistors) or on the modulation of charge in a resistive channel (field effect transistors). In contrast to this, the present device can be compared to a hypothetical vacuum diode whose cathode has an effective electron temperature which is controlled without inertia by an input electrode (cathode heater). The device has been implemented in an AlGaAs/GaAs heterojunction structure. One of the conducting layers is realized as an FET channel, the other as a heavily doped GaAs substrate. The layers are separated by an Al x Ga 1 - x As graded barrier. Application of a source-to-drain field leads to a heating of channel electrons and charge injection into the substrate. The substrate thus serves as an anode and the FET channel represents a hot-electron cathode, whose effective temperature is controlled by the source-to-drain field. Operation of the charge injection transistor is studied at 300, 77, and 4.2 K. At 77 K the existence of power gain is demonstrated experimentally with the measured value of the mutual conductance g m reaching 280 mS/mm (at 300 K, g m ≈ 88 mS/mm). The fundamental limit on the device speed of operation is analyzed and shown to be determined by the time of flight of electrons across a high-field region of spatial extent ∼ 10-5cm. Practical ways of approaching this limit are discussed. The process of hot-electron injection from the channel is studied experimentally at 77 and 4.2 K with the purpose of measuring the electron temperature in the channel at different bias conditions. For not too high substrate bias the electron temperature in the channel is found to be proportional to the square of the heating voltage.

Novel real-space hot-electron transfer devices

A new class of devices based on hot-electron transfer between two conducting layers is proposed. The essential feature of these devices is a pronounced negative differential resistance (NDR) in the drain circuit, controlled by gate and substrate voltages. This allows a novel type of bistable logic element, which, although being unipolar, is comparable to the CMOS inverter in that a significant current is drawn only during switching. Another possible application is a gate-controlled microwave generator and amplifier. In the present work, the above device concepts are analyzed in the instance of GaAs/ GaAlAs heterojunction realizations.