JPH0739250Y2 - Semiconductor structure - Google Patents

Description

Detailed Description of the Invention (a) Field of Industrial Application The present invention intends to provide a semiconductor structure capable of obtaining a dislocation-free crystal thin film on GaAs in which generation of dislocations caused by lattice mismatch is suppressed. To do.

(B) Conventional technology It is well known that information transmission, processing and recording / reproducing technology using light is becoming an important research and development subject at present, and it is well known that semiconductor lasers, light emitting diodes and solid or liquid Research on light-emitting devices has been advanced, and some have already reached the stage of practical application.

Among these, a blue light emitting diode (blue LED) is one that is urgently desired to be put into practical use. Blue LED materials include gallium nitride (GaN), silicon carbide (SiC), zinc selenide (ZnSe) and zinc sulfide (ZnS). Among these materials, GaN and ZnS are expected to be semiconductor laser materials capable of oscillating not only blue LEDs but also ultraviolet rays because they have a direct transition type band structure having a bandwidth of 2.7 eV or more at room temperature.

By the way, when growing a ZnSe single crystal film on a GaAs substrate,
When the grown film thickness exceeds 150 nm, dislocations occur in the ZnSe film due to the lattice mismatch between GaAs and ZnSe.

Therefore, in order to suppress the occurrence of such dislocations, about 5% of S is added to ZnSe to form a ternary mixed crystal ZnSe _1-χ Sχ (χ
0.05) to make a lattice match with a GaAs substrate, or a method of using a ternary mixed crystal InGaAs lattice-matched to ZnSe by adding In as a substrate (for example, IEICE Technical Report, SSD85-162, See P59-67).

(C) Problems to be solved by the invention In the above-mentioned conventional technique, a mixed crystal was used to match the crystal lattices of the growth film and the substrate. However, in forming such a mixed crystal, the composition ratio Is difficult to control accurately.

The present invention has been made in view of the above-mentioned drawbacks, and it is difficult to control the composition ratio.It does not form a lattice-matched mixed crystal and suppresses the generation of dislocations caused by lattice mismatch. It is intended to provide a semiconductor structure capable of obtaining

(D) Means for solving the problem The present invention is a semiconductor structure in which a ZnSe single crystal film having a thickness of 150 nm or less and several atomic layers of ZnS or ZnSeS mixed crystal are alternately laminated on a GaAs substrate.

(E) Action The ZnSe film grown on the GaAs substrate is within the elastic limit and the dislocation does not occur if the film thickness is 150 nm or less. The ZnSe film is Ga
The lattice constant is larger than As, and the ZnSe film receives compressive stress from the GaAs substrate, but ZnS and ZnSeS have smaller lattice constants than ZnSe, so inserting a ZnS layer or ZnSeS layer into the ZnSe layer causes dislocations. Can relieve compressive stress.

(F) Example FIG. 1 is a cross-sectional view of a semiconductor structure of an example of the present invention, which is formed by growing on a GaAs substrate having a plane orientation (100) by using molecular beam epitaxy (MBE). To be done.

Here, the MEB method will be described below.

Since the MEB method is handled in an ultra-high vacuum system of 10 ^-10 Torr or more, the molecules have a long mean free path, and the gas molecules generated from the ejection cell fly to the substrate as a molecular flow. After reaching the substrate, the molecules diffuse on the surface and then associate and bond with other molecules to be trapped on the surface of the substrate for deposition and growth. Molecules that do not contribute to association / bonding are desorbed and re-evaporated from the substrate surface. The number of molecules reaching the surface of the substrate is equal to the molecular beam intensity, and the molecular beam intensity is uniquely determined by the temperature of the evaporation source. The crystal growth rate, the impurity concentration, and the composition ratio of the multi-component compound can be controlled by the molecular beam intensity.

FIG. 2 shows a schematic diagram of a general molecular beam epitaxial growth apparatus, in which (4) is a chamber, the inside of which is adjusted to about 10 ⁻¹⁰ Torr by ultra-high vacuum exhaust from the exhaust part (5). Reference numeral (1) shows a GaAs substrate arranged in the chamber (4), and its heating amount is adjusted by a resistance heater (not shown). (6), (7), and (8) show the first, second, and third cells in which Zn, Se, and ZnS are placed, respectively, and the respective temperatures are variably set.

Using such a molecular beam epitaxial growth system,
In order to form the dislocation-free crystal thin film shown in the figure, first, GaAs
A substrate (1) having a plane orientation of <100> is used, and surface treatment is performed by thermal etching at a temperature of 620 ° C. for 15 minutes before growth. Then, the temperature of the substrate (1) is set to 320 ° C., and the temperatures of the first and second cells (6) and (7) are heated to about 300 ° C. and about 220 ° C. to form the ZnSe film (2). Grow 100 nm (deposition rate is 1 μm / h). Then, Z on the ZnSe film (2)
The nS film (3) is grown to a thickness of 2 nm (film formation rate is 0.3 μm / h, temperature of the third cell (8) is 950 ° C.). Furthermore, as in the above, Z
By repeatedly growing the ZnSe film (2) and the ZnS film (3) on the nS film (3), a thin film having a laminated structure of the ZnSe film (2) and the ZnS film (3) is formed.

Since the ZnSe film (2) has a larger lattice constant than the GaAs substrate (1), it receives compressive stress from the GaAs substrate (1), but since the ZnS film (3) has a smaller lattice constant than the ZnSe film (2), the ZnS film (3) ) Is inserted between the ZnSe films (2), the compressive stress that causes dislocation generation can be relaxed.

The dislocations can be confirmed by examining the lattice image with a transmission electron microscope.

Although the ZnS film is used in this embodiment, ZnSeS may be used.

(G) Effect of the Invention As is clear from the above description, the present invention is a ZnSe single crystal layer with a thickness of 150 nm or less and a few atomic layers of ZnS or Zn on a GaAs substrate.
By disposing SeS mixed crystals alternately, it is possible to obtain a dislocation-free crystal thin film on a GaAs substrate in which dislocation generation is suppressed.

[Brief description of drawings]

FIG. 1 is a sectional view of a semiconductor structure of an embodiment of the present invention, and FIG. 2 is a sectional view of a molecular beam epitaxial device. (1) …… GaAs substrate, (2) …… ZnSe film, (3) …… Zn
S film, (4) ... Chamber, (5) ... Exhaust part, (6)
(7) (8) …… Cell.

Claims (1)

[Scope of utility model registration request] 1. A semiconductor structure characterized in that a ZnSe single crystal layer having a thickness of 150 nm or less and several atomic layers of ZnS or ZnSeS mixed crystal are alternately laminated on a GaAs substrate.