CN1309094C - Hole resonance tunnel-through diode based on Si/SiGe - Google Patents

Abstract

The invention discloses a hole type resonant tunneling diode based on Si/SiGe, which belongs to the field of novel semiconductor devices and nanometer electronic devices. A strained SiGe layer is used as a hole quantum well, and Si is used as a hole barrier to form a hole double barrier single quantum well structure. Highly doped P-type Si is used as the substrate, and the undoped SiGe layer, Si layer, SiGe layer, Si layer, and SiGe layer are sequentially deposited on the substrate by chemical vapor deposition or molecular beam epitaxy. And the mesa structure formed by heavily doped P-type Si, and the electrodes formed on the substrate and the mesa structure respectively. The experiment proves that the obvious differential negative resistance phenomenon can be observed by testing the current-voltage characteristics of the sample at room temperature. The manufacturing process is compatible with the current mainstream Si semiconductor planar process, and can more effectively improve the integration level of integrated circuits.

Description

Hole-Type Resonant Tunneling Diode Based on Si/SiGe

technical field

The invention belongs to the field of novel semiconductor devices and nanometer electronic devices, in particular to a hole-type resonant tunneling diode based on Si/SiGe.

Background technique

With the continuous development of silicon-based VLSI planar process technology, the feature size of microelectronic devices is shrinking and approaching its physical limit. At this size scale, quantum effects in microelectronic devices will dominate carrier transport and device operation. Such semiconductor devices whose feature size is on the order of nanometers and which utilize quantum effects are generally called nanometer quantum devices. For example: quantum dot devices, single electron devices, resonant tunneling diodes, etc. Among them, the resonant tunneling diode is more favored by many researchers because of its relatively mature manufacturing process and unique differential negative resistance characteristics. Using it in the circuit design of high-frequency oscillators, multi-value logic circuits and memory circuits can effectively reduce the number of device units in the circuit and reduce the chip area. Therefore, resonant tunneling diodes are recognized as one of the most promising nanometer quantum devices.

US Patent No. 6,229,153 discloses a method for preparing a resonant tunneling diode using GaAs/AlGaAs/InGaAs materials. However, this method has problems such as high cost and incompatibility with the current mainstream Si semiconductor planar process, which greatly limits its application.

The invention proposes a hole-type resonant tunneling diode based on Si/SiGe. Its manufacturing process is compatible with the current mainstream Si semiconductor planar process, and can more effectively improve the integration of integrated circuits. The principle of using Si/SiGe materials to make hole-type resonant tunneling diodes is as follows: When the thickness of the SiGe strained layer epitaxially grown on the Si substrate is less than its critical thickness, the energy band between the relaxed Si and the strained SiGe is discontinuous It mainly appears in the valence band, and the conduction band is approximately continuous. We use this discontinuity of the valence band to construct the double-barrier single quantum well structure required for the hole-type resonant tunneling diode.

Contents of the invention

The object of the present invention is to propose a hole-type resonant tunneling diode based on Si/SiGe. It is characterized in that a strained SiGe layer is used as a hole quantum well, and undoped Si is used as a hole barrier. Its main components are: highly doped P-type Si substrate, on which undoped SiGe layer, Si layer, SiGe layer, Si layer are sequentially deposited by chemical vapor deposition method or molecular beam epitaxy method. , a SiGe layer and a mesa structure formed by heavily doped P-type Si, and electrodes formed by sputtering metal on the substrate and the mesa structure respectively. The beneficial effect of the present invention is that it has been proved by experiments that it achieves the expected purpose, and an obvious differential negative resistance phenomenon can be observed at room temperature. The manufacturing process is compatible with the current mainstream Si semiconductor planar process, and can more effectively improve the integration level of integrated circuits.

Description of drawings

Figure 1a is a schematic diagram of the structure of a hole-type resonant tunneling diode based on Si/SiGe.

Figure 1b is the energy band diagram corresponding to Figure 1a.

Figure 2a. Schematic diagram of the energy levels of the valence band under the bias voltage of O.

Figure 2b is a schematic diagram of the energy level of the valence band under Va.

Figure 2C is a schematic diagram of the energy level of the valence band under Vb.

Fig. 2d is a schematic diagram of the current-voltage relationship curve of a hole-type resonant tunneling diode based on Si/SiGe.

FIG. 3 is a graph showing the current-voltage relationship of the tested hole-type resonant tunneling diode based on Si/SiGe.

Detailed ways

Figure 1a shows a schematic diagram of the structure of a hole-type resonant tunneling diode based on Si/SiGe. Using a double-barrier single quantum well structure, on a heavily doped P-type (doping concentration required to be greater than 1E+19cm ^-3 ) Si substrate 7, the following layers are sequentially grown by chemical vapor deposition: the thickness is 8nm-20nm SiGe layer 1, wherein Ge accounts for 0.2-0.5% by volume, as the first spacer region; Si layer 2 with a thickness of 1nm-6nm, as the first barrier region; SiGe layer 3 with a thickness of 2nm-6nm, wherein Ge accounts for 0.2-0.5% by volume, as a quantum well region; a Si layer 4 with a thickness of 2nm-6nm is used as a second potential barrier region; a SiGe layer 5 with a thickness of 8nm-20nm, wherein Ge occupies a volume ratio of 0.2- 0.5%, as the second spacer region; a heavily doped P-type (doping concentration greater than 1E+19cm ^-3 ) Si layer 6 with a thickness of 1um-3um is used as a contact layer for making electrode leads.

The energy band diagram corresponding to the structure shown in Figure 1a is shown in Figure 1b. When the thickness of the SiGe strained layer epitaxially grown on the Si substrate is less than its critical thickness, the energy band discontinuity between relaxed Si and strained SiGe mainly appears in the valence band, and the conduction band is approximately continuous. The band gap of bulk Si is higher than that of strained SiGe, so the Si layer is used as hole barrier layers 2 and 4; the strained SiGe layer is used as hole quantum well region 3 (as shown in Figure 1b). Because the SiGe layer used as the quantum well region 3 is very thin, close to the order of de Broglie wavelength of electrons, the energy level of holes in the well is split into several discrete energy levels according to the quantum effect. In Fig. 2a, the situation of thermal equilibrium state is given when the bias voltage is zero. When the bias voltage is increased, a hole accumulation region is formed near the barrier on the anode side and a depletion region is formed on the cathode side near the barrier. Only very few holes are able to tunnel through the double barrier. Once the bias voltage reaches the value of Va, the energy state occupied in the valence band on the anode side is flush with the E1 empty energy state in the quantum well, and resonance tunneling occurs at this time, as shown in Figure 1b and Figure 2b. At this point, many holes are able to tunnel through the left barrier layer 2 into the quantum well region 3 and then tunnel through the right barrier layer 4 into unoccupied energy states in the valence band on the cathode side. When the bias voltage is further increased to Vb, the valence band edge on the left in Figure 2a rises above E1, and the number of electrons that can tunnel through the potential barrier decreases sharply, as shown in Figure 2c. The valley current is mainly the current component originating from excess carriers, which increases with bias voltage. Phonon-assisted or impurity-assisted tunneling also contributes to this current. The schematic diagram of the current-voltage relationship curve of the hole-type resonant tunneling diode based on Si/SiGe is shown in Figure 2d.

The preparation process of the hole-type resonant tunneling diode based on Si/SiGe is as follows:

1. Vapor deposition of various layers of thin films on the prepared heavily doped P-type substrate 7;

2. Etching the epitaxial material by RIE dry method to obtain the mesa structure;

3. grow a layer of SiO ₂ as insulating layer 8 by LPCVD;

4. Electrode contact holes are etched out by wet etching after photolithography;

5. Sputtering aluminum film as electrode lead;

6. Photolithography, etching out the substrate electrode 9 and the mesa electrode 10, and alloying.

If we apply a voltage between the mesa electrode 10 and the substrate electrode 9 to test the current flowing through the unit, we can obtain the current-voltage relationship curve of the unit. The current-voltage relationship curve of the hole-type resonant tunneling diode sample based on Si/SiGe is shown in Figure 3, and the shape of the curve is similar to the current-voltage relationship curve shown in Figure 2d.

Claims (1)

1. cavity type resonance tunnel-through diode based on Si/SiGe, it is characterized in that: do the hole quantum well with the strain SiGe layer, do the hole potential barrier with Si, form the double potential barrier single quantum in hole, make substrate with highly doped P type Si, the mesa structure that unadulterated SiGe layer, Si layer, SiGe layer, Si layer, SiGe layer and heavily doped P type Si form on methods such as employing chemical gas-phase deposition method or molecular beam epitaxy on this substrate deposit successively, and on substrate, form electrode respectively with the mesa structure splash-proofing sputtering metal.

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