Group IIIV Semiconductor Growth Parameters

Group III-V semiconductors are the major materials used in optoelectronic and high-frequency electronic device applications. The ability to tailor the band structure and lattice constant in ternary and quaternary alloys by varying the composition represents one of the desirable features of these materials.

The GaAs-based materials described below include not only GaAs, but gallium indium phosphide (GaInP), gallium aluminum arsenide (GaAlAs), and gallium indium arsenide phosphide (GaInAsP).

GaAs layers can be grown either at atmospheric or low pressure in the temperature range from 500 to 550 °C (Ref 52). TEGa or TMGa and AsH3 have been used as gallium and arsenic sources. Pure hydrogen can be used as a carrier gas. The growth rate depends linearly on the flow rate of Group III (gallium) elements and is independent of AsH3 flow rate, substrate temperature, and substrate orientation. This suggests that epitaxial growth is controlled by the mass transport of Group III species.

The growth of GaAs layers has been carried out on <100> GaAs substrates misoriented up to 2° toward the <011> plane. The substrates were etched in a H2SO4:H2O2:H2O (5:1:1) solution for 20 s at 40 °C (105 °F), rinsed with deionized water, and dried under pure nitrogen. Before the growth process, the substrates were initially heated to the growth temperature under hydrogen and AsH3 for 5 min to remove any surface oxides. Table 3 lists the optimum conditions for the low-pressure MOCVD growth of GaAs.

Table 3 Optimum growth conditions of gallium arsenide (GaAs), gallium indium phosphide (GaInP), and gallium indium arsenide phosphide (GaInAsP)

GaAs

Ga0.51In0.49P

Ga0.87In0.13As0.73P0.27

Growth pressure, Pa (torr)

10,130 (76)

10,130 (76)

10,130 (76)

Growth temperature, °C (°F)

510 (950)

510 (950)

510 (950)

Total hydrogen flow rate, L/min (gal/min)

3 (0.8)

3 (0.8)

3 (0.8)

Arsine, cm3/min (in.3/min)

30 (1.8)

20 (1.2)

Trimethylindium, cm3/min (in.3/min)

200 (12)

150 (9)

Triethylgallium, cm3/min (in.3/min)

120 (7)

120 (7)

170 (10)

Phosphine, cm3/min (in.3/min)

300 (18)

200 (390)

Growth rate, nm/min (^in./min)

15 (0.6)

20 (0.8)

25 (1.0)

Epitaxial GaAs layers are of the «-type in a wide range of Group V/III ratios and substrate temperatures. Suitable conditions, such as growth temperature, growth rate, total flow rate, purity of starting materials, and reactor design, are responsible for the high quality of the epitaxial layers.

GaInP layers can be grown on GaAs using MOCVD, either at atmospheric pressure or low pressure, in the temperature range from 500 to 600 °C (930 to 1110 °F) (Ref 137). Different Group III alkyls can be used for gallium and indium sources, whereas hydrides or alkyls can be used for the Group V phosphorus source. Chemical reactions that occur among these sources are:

0.5 LR3Ga + 0.49 i?'3In + EH3 -Gao.51Ino.49P + //C„H2„

where R, R\ and E can be methyl, ethyl, alkyl, or hydride. For example, one can use:

0.49(C2H5)3In + 0.51(C2H5)3Ga + PH3 -> InGaP + «C2H6, or

0.49(CH3)3In + 0.51(CH3)3Ga + PH3 InGaP + «CH4, or

0.49(CH3)3In + 0.51(C2H5)3Ga + PH3 InGaP + «C2H6, or

0.49(C2H5)3In + 0.51(CH3)3Ga + PH3 -> InGaP + «C2H6

The GaInP layers can be grown at the lower temperatures of 500 to 550 °C (930 to 1020 °F), by using TEGa, TMIn, and PH3 in a hydrogen carrier gas. At optimum conditions (Table 3), the growth rate (dx/dt) of GaInP depends on the flow rates of TMIn and TEGa and is independent of the PH3 flow rate and growth temperature. The undoped GaInP layer grown as specified has a free electron carrier concentration of 5 x 1014/cm3 (80 x 1014/in.3), with a mobility of 6000 cm2/V • s (930 in.2/V • s) at 300 K and 40,000 cm2/V • s (6200 in.2/V • s) at 77 K. No GaAs buffer layer was grown in this case.

GaAlAs layers can be grown on a GaAs substrate in the temperature range of 600 to 750 °C (1110 to 1380 °F) by using TMGa, TMAl, and AsH3 as the sources of gallium, aluminum, and arsenic, respectively. Oxygen incorporation, produced by the strong reactivity of aluminum with oxygen, can deteriorate the optical and electrical properties of the GaAlAs epitaxial layer (Ref 138). To solve this problem, graphite baffles are used for internal gettering. They absorb TMAl, which then reacts with oxygen to form the extremely stable, nonvolatile Al2O3 (Ref 139). It was later discovered that high-quality aluminum gallium arsenide (AlGaAs) can be grown at higher temperatures (<780 °C, or 1440 °F) without using oxygen-gettering techniques (Ref 140). This is because the aluminum suboxide that absorbs on surfaces at high temperatures is more volatile. It was demonstrated that at low aluminum concentrations, the photoluminescence intensity increases by three orders of magnitude as the substrate temperature increases from 600 to 750 °C (1110 to 1380 °F). No effect occurs at high aluminum concentrations (Ref 141).

GaInAsP layers can be grown on GaAs by using low-pressure MOCVD within the entire composition range in which the quaternary is lattice matched to GaAs. Both TMIn and TEGa are used as the sources of indium and gallium, whereas AsH3 and PH3 are used as the sources of arsenic and phosphorus. The optimum conditions for the growth of GaInAsP (composition having a bandgap of 808 nm, or 31.5 pin.) on GaAs are listed in Table 3. The quality of the quaternary is comparable with that of the quaternary grown on InP substrates (Ref 142).

The InP-based materials described below include not only InP, but gallium indium arsenide (GaInAs) and gallium indium arsenide phosphide (GaInAsP) grown on InP.

High-quality InP layers have been grown by using MOCVD (Ref 52). Both TEIn and PH3 are used as indium and phosphorus sources, respectively. A mixture of hydrogen and nitrogen is used as the carrier gas. The presence of hydrogen is necessary to avoid the deposition of carbon, and the presence of nitrogen is necessary to avoid the parasitic reaction between TEIn and PH3.

The InP layers have been grown at 10 kPa (76 torr) and at low temperatures (between 500 and 650 °C, or 930 and 1200 °F) by using TEIn, PH3, and a mixture of hydrogen and nitrogen as the carrier gas. The growth rate (ranging from 200 to 800 cm3/min, or 12 to 48 in.3/min) is linearly dependent on the TEIn flow rate, and is independent of PH3 flow rate, substrate temperature, and substrate orientation. This suggests that epitaxial growth is controlled by the mass transport of Group III species.

Razeghi and Duchemin (Ref 18) have studied the growth of InP layers by using 100% hydrogen and mixtures of hydrogen and nitrogen as the carrier gas. The best morphology and the highest photoluminescence intensity were obtained by using 50% hydrogen and 50% nitrogen. Using argon instead of nitrogen produced InP layers with the same surface quality. Table 4 lists the optimum conditions used in this study for the MOCVD growth of InP in the temperature range of 550 to 650 °C (1020 to 1200 °F). The InP layers grown by MOCVD are less compensating at lower growth temperatures.

Table 4 Optimum growth conditions of indium phosphide

Growth temperature

Nitrogen-triethylindium bubbler flow rate

Phosphine flow rate

Total flow rate

Growth rate

°C

°F

cm3/min

in.3/min

cm3/min

in.3/min

L/min

gal/min

nm/min

^iin./min

550

1020

450

27

260

16

6

1.6

20±1

0.S±0.04

225

14

200

12

6

1.6

10±1

0.4±0.04

650

1200

450

27

520

32

6

1.6

22±1

0.9±0.04

225

14

400

24

6

1.6

11±1

0.4±0.04

GaInAs layers can be grown on InP substrates at 10 kPa (76 torr) in the temperature range of 500 to 650 °C (930 to 1200 °F), using either TEIn or TMIn, TEGa, and AsH3 (Ref 52). When TEIn is used as the indium source, then pure hydrogen is used as the carrier gas. When TMIn is used, then a mixture of hydrogen and nitrogen is used as the carrier gas. The growth rate is linearly dependent on the combined flow rates of TEGa and TEIn. It is independent of the AsH3 flow rate within the range of 60 to 90 cm3/min (3.5 to 5.5 in.3/min). This suggests, as in the case of InP, that epitaxial growth is controlled by the mass transport of Group III species. Uniform layers of Gao.47In0.53As have been deposited over large areas (10 cm2, or 1.5 in.2) of InP substrates. The quality of the epitaxial layer is sensitive to the alloy composition, as in the case of GaInAs grown by other techniques.

The surface morphology of GaInAs grown on InP depends on the pretreatment of the substrate and is independent of the lattice mismatch, even when the mismatch is 0.01 or more. Ga0.47In0.53As grown on InP exhibits an excellent surface morphology and state-of-the-art electron mobility when grown under the optimum conditions listed in Table 5.

Table 5 Optimum growth conditions of gallium indium arsenide/indium phosphide

Growth temperature, °C (°F)

550 (1020)

Total flow rate, L/min (gal/min)

7 (1.8)

Hydrogen-triethylindium bubbler flow rate, cm3/min (in.3/min)

450 (27)

Hydrogen-triethylgallium bubbler flow rate, cm3/min (in.3/min)

180 (11)

Phosphine flow rate, cm3/min (in.3/min)

90 (5)

Growth pressure, Pa (torr)

76 (0.6)

Growth rate, nm (|^in.)

27 (1.05)

Note: Stoichiometry of material is Gao.47Ino.53As.

Note: Stoichiometry of material is Gao.47Ino.53As.

GaxIn1-xAsyP1-y layers can be grown on InP substrates in the range of compositions that are lattice matched. Growth occurs at 10 kPa (76 torr) and at a substrate temperature between 630 and 650 °C (1170 and 1200 °F) using TEIn, TEGa, AsH3, and PH3 in a mixture of hydrogen and nitrogen carrier gas (Ref 52). The growth rate is linearly dependent on the sum of the partial pressures of TEIn and TEGa, and is independent of the arsenic and phosphorus partial pressures. The epitaxial layer quality is sensitive to the pretreatment of the substrate and the alloy composition. The optimum growth conditions for the lattice-matched composition, Ga0.23In0.77As0.5iP0.49, are listed in Table 6.

Table 6 Optimum growth conditions of gallium indium arsenide phosphide/indium phosphide

Source

Partial pressure

Temperature

Pa

mbar

°C

°F

Triethylindium

0.85

0.0085

31

88

Triethylgallium

0.3

0.003

0

32

Arsine

31

0.31

25

77

Phosphine

700

7

25

77

nitrogen, 7 L/min (1.8 gal/min). Stoichiometry of material is Ga0.28Ina72As0.61P0.39.

Source: Ref 52

The nitride semiconductors described below include gallium nitride (GaN) and aluminum nitride (AlN).

High-quality GaN films have been very difficult to obtain because of the large mismatch in lattice constant and coefficient of thermal expansion with available substrates. The (001) plane of sapphire is often used, although the mismatch is large. Sun et al. recently discovered that the (012) plane is better matched with GaN and produces higher-quality GaN films (Ref 143). In the cited study, GaN was grown at atmospheric pressure in the temperature range of 900 to 1000 °C (1650 to 1830 °F), using TMGa and ammonia (NH3) as the sources of gallium and nitrogen. The carrier gas was hydrogen. The precursors were mixed just before entering the reactor, in order to reduce the parasitic reactions between the metal-organics and NH3. The total gas flow rate of 1600 sccm comprised 3 to 10 standard cm3/min (sccm) TMGa, 500 to 1100 sccm NH3, and carrier gas. The bubbler was kept at -10 °C (15 °F) for TMGa.

Aluminum nitride has been grown by using atmospheric-pressure MOCVD, with TMAl and NH3 as the aluminum and nitrogen sources, respectively. The flow rates of each precursor were: 5 sccm of TMAl, 400 sccm of NH3, and 1200 sccm of N2. The TMAl was maintained in a bubbler at 25 °C (77 °F). The growth temperature was 1050 °C (1920 °F). Both the (001) and (012) planes of sapphire and the (100) plane of silicon were used as substrates. Thermal annealing under hydrogen and nitrogen caused no degradation of the crystalline quality, and improved the optical quality of the films (Ref 144).

The antimony-based materials described below include indium antimonide (InSb) and indium thallium antimonide (InTlSb).

Indium antimonide can be grown by using low-pressure MOCVD, with TMIn and trimethylantimony (TMSb) as sources for indium and antimony, respectively (Ref 145). Both InSb and GaAs (100) substrates were used in the growth process. Optimum growth conditions are listed in Table 7. The full width at half maximum of an x-ray rocking curve of 174 arc • s and a Hall mobility of 76,200 cm2/V • s (11,820 in.2/V • s) at 240 K have been observed for a layer of 4.85 pm (190 pin.) grown under the optimum conditions.

Table 7 Optimum growth conditions of indium antimonide

Growth pressure, Pa (torr)

10,130 (76)

Growth temperature, °C (°F)

465 (870)

Total hydrogen flow rate, L/min (gal/min)

1.5 (0.40)

Hydrogen flow rate through trimethylindium bubbler, cm3/min (in.3/min)

50 (3.1)

Hydrogen flow rate through trimethylantimony bubbler, cm3/min (in.3/min)

20 (1.2)

Growth rate, ^m/h (^in./h)

1.2 (47)

Source: Ref 145

Source: Ref 145

Indium thallium antimonide was grown for the first time by using low-pressure MOCVD, with TMIn and TMSb as sources of indium and antimony, respectively, and cyclopentadienylthallium as the source of thallium (Ref 146). The optimum growth conditions are listed in Table 8.

Table 8 Optimum growth conditions of indium thallium antimonide

Growth pressure, Pa (torr)

10,130 (76)

Growth temperature, °C (°F)

455 (851)

Total hydrogen flow rate, L/min (gal/min)

1.5 (0.4)

Hydrogen flow rate through trimethylindium bubbler, cm3/min (in.3/min)

50 (3.1)

Hydrogen flow rate through trimethylantimony bubbler, cm3/min (in.3/min)

20 (1.2) 60 (3.7)

Source: Ref 146

Other Group III-V materials that have been grown by using MOCVD are listed in Table 9. Table 9 The principal Group III-V materials grown by metal-organic chemical vapor deposition

Film

Substrate

Precursors

Reference

Gallium phosphide

Gallium phosphide

TMG, PH3

147

Gallium antimonide

Gallium antimonide

TMG, TMSb

148

Indium arsenide

Indium arsenide

TEI, AsH3

149

Gallium aluminum phosphide

Gallium phosphide

TMG, TMAl, PH3

147

Gallium aluminum antimony

Gallium arsenide

TMG, TMAl, TMSb

150

Gallium indium arsenide

Gallium arsenide

TMG, TEI, TMAs

151

Aluminum indium arsenide

Indium phosphide

TMAl, TMI, AsH3

152

Indium arsenide antimonide

Indium antimonide

TMI, TMSb, AsH3

153

Gallium aluminum arsenide antimonide

Gallium arsenide

TMG, TMAl, TMAs, TMSb

151

Indium arsenide antimonide phosphide

Indium arsenide

TEI, TESb, AsH3, PH3

154

Note: TMG, trimethylgallium; PH3, phosphine; TMSb, trimethylantimony; TEI, triethylindium; AsH3, arsine; TMAl, trimethylaluminum; TMAs, trimethylarsenic; TMI, trimethylindium; TESb, triethylantimony

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