JPS6359267B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD OF THE INVENTION The present invention relates to an improvement in a compound semiconductor device having a heterojunction structure and capable of high-speed operation using two-dimensional electron gas. Conventional technology and problems Conventionally, this type of compound semiconductor device has two
The structure is such that a shot metal gate electrode is directly formed on an n-type Al _x Ga _1-x As electron supply layer that supplies dimensional electron gas. FIG. 1 shows an energy band model of the compound semiconductor device, in which 1 is a shot metal gate electrode, 2 is an n-type Al _x Ga _1-x As electron supply layer, 3 is a non-doped GaAs semiconductor substrate, and 4 is a non-doped GaAs semiconductor substrate. It is a two-dimensional electron gas layer. The electron barrier potential of the gate electrode 1 in this compound semiconductor device is determined by the shot barrier φ _B , which is the difference in work function between the shot metal and the n-type Al _x Ga _1-x As crystal. As is well known, the forward voltage that can be applied to the gate electrode 1 must be maintained within a range that does not exceed the shot barrier φ _B , and in the compound semiconductor device, it is approximately 0.8 [V] at most. Due to the structure of the epitaxially grown semiconductor layer, it is generally impossible to artificially control the electron barrier. Therefore, the tolerance of the applied gate bias voltage is small, and even if it is desired to increase the threshold voltage in, for example, a switching semiconductor device, a high frequency semiconductor device, etc., it is difficult to achieve this. Purpose of the Invention The present invention is to make the gate electron barrier potential in the compound semiconductor device as described above variable, so that it is possible to obtain such a compound semiconductor device having a desired gate electron barrier potential as necessary. . Structure of the Invention The present invention provides a structure of an epitaxially grown semiconductor layer in _a compound semiconductor device having _a heterojunction structure _. A Ga _1-y As (1≧y≧0) barrier adjustment layer is formed. This barrier adjustment layer is not used as a pn junction, but merely serves to control the electron barrier by ionizing electrons in the barrier adjustment layer. When such an epitaxially grown semiconductor layer structure is adopted, the resulting electron barrier is not the shot barrier φ _B at the shot metal-semiconductor crystal interface, but the p
It is determined by the potential barrier formed in the type Al _y Ga _1-y As barrier adjustment layer. FIG. 2 shows an energy band model of such a compound semiconductor device, and in the figure, 11 is a shot metal gate electrode, 12 is a p-type Al _{y Ga 1-y As barrier adjustment layer, and 13 is a p-type Al y} Ga _1-y As barrier adjustment layer. is n-type Al _x
14 represents a non-doped GaAs semiconductor substrate, and 15 represents a two _- dimensional electron gas layer. The potential barrier obtained here is p-type Al _y
It is determined by three physical constants: the thickness of the Ga _1-y As barrier adjustment layer 12, the amount of p-type impurity doping, and the y value, and the minimum is the shot barrier φ _B (~0.8 [eV]) obtained with the conventional configuration. ) to a maximum of around 2.1 [eV], which is about the band gap of AlAs. Therefore, the forward voltage at the gate electrode 11 can be dramatically increased compared to the conventional case. p that controls only such potential barriers
Impurity doping amount of type Al _y Ga _1-y As barrier adjustment layer 12
The relationship between Na and film thickness t is given by the following equation when the y value of the barrier adjustment layer 12 is constant and the y value and the x value of the n-type Al _x Ga _1-x As electron supply layer 13 are the same. It will be done. Here, Eg is the energy gap of Al _y Ga _1-y As, and N _D is the doping amount of the n-type Al _x Ga _1-x As electron supply layer 13. Note that it is effective to prevent surface oxidation by grading the distribution of Al so that the y value in the p-type Al _y Ga _1-y As barrier adjustment layer 12 is 0 at the surface, that is, it is terminated with GaAs. be. Embodiment of the Invention FIG. 3 is a cutaway side view of essential parts of an embodiment of the invention. In the figure, 21 is a non-doped GaAs semiconductor substrate, 22 is a two-dimensional electron gas layer, and 23 is an n-type Al _x
Ga _1-x As electron supply layer, 24 p-type Al _y Ga _1-y As barrier adjustment layer, 25 n ⁺ type GaAs electrode contact layer,
Reference numeral 26 indicates an aluminum gate electrode, and reference numeral 27 indicates a gold/germanium/gold (Au.Ge/Au) ohmic electrode. In this embodiment, an n ⁺ type electrode contact layer 25 is provided below the ohmic electrode 27 in order to reduce contact resistance, and the ohmic alloy layer of the electrode metal and GaAs crystal extends to the two-dimensional electron gas layer 22. It has been reached. Next, the main specifications are listed as follows. Non-doped GaAs semiconductor substrate 21 Thickness: approximately 1 [μm] N-type Al _x Ga _1-x As electron supply layer 23 Thickness: approximately 500 [Å] Impurity concentration: 1×10 ¹⁸ [cm ^-3 ] x Value: 0.3 P-type Al _y Ga _1-y As barrier adjustment layer 24 Thickness: About 100 to 300 [Å] Impurity concentration: 2×10 ¹⁸ [cm ^-3 ] y value: 0≧y≧0.3 In this example The electron barrier potential directly below the gate electrode 26 is as shown in FIG. In Figure 4, the vertical axis represents the electron barrier potential in units [eV], and the horizontal axis represents the p-type Al _y Ga _1-y As barrier adjustment layer 2.
The thickness of 4 is measured in the unit [Å]. As is clear from the figure, the electron barrier potential in this example is observed to be approximately 0.8 to 1.2 [eV]. This is much larger than the conventional value. Effects of the Invention The present invention provides a compound semiconductor device having a heterojunction and capable of high-speed operation using _two -dimensional _electron gas.
By forming a type Al _y Ga _1-y As barrier adjustment layer,
The electron barrier potential is calculated from the shot barrier φ _B.
Energy gap Eg of Al _y Ga _1-y As barrier adjustment layer
As a result, the range of dynamic characteristics of the compound semiconductor device can be expanded.

[Brief explanation of the drawing]

Figure 1 shows the conventional energy band model.
Fig. 2 shows an energy band model when the present invention is applied, Fig. 3 is a cutaway side view of essential parts of an embodiment of the present invention, and Fig. 4 shows electron barrier potential and p-type Al _y Ga _{1- y} is a diagram showing the relationship with the thickness of the As barrier adjustment layer. In the figure, 21 is a non-doped GaAs semiconductor substrate, 22 is a two-dimensional electron gas layer, and 23 is an n-type Al _x
Ga _1-x As electron supply layer, 24 p-type Al _y Ga _1-y As barrier adjustment layer, 25 n ⁺ type GaAs electrode contact layer,
26 is an aluminum gate electrode, and 27 is a gold/germanium/gold ohmic electrode.

Claims (1)

[Claims] 1 Has a heterojunction structure of AlGaAs/GaAs 2
In a compound semiconductor device that performs high-speed operation using dimensional electron gas, a p-type Al _y Ga _1-y As (1≧y≧0) barrier adjustment layer is provided on the n-type AlGaAs electron supply layer, A shot gate electrode is provided on the surface of the type Al _y Ga _1-y As (1≧y≧0) barrier adjustment layer, and furthermore, Al is distributed on the surface so that it is terminated with GaAs at y=0. A compound semiconductor device characterized by: