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Metalorganic Vapor-Phase Epitaxy (MOPVE)

Published Date
Author Cadence PCB Solutions

Key Takeaways

  • MOVPE is essential for creating high-quality, crystalline semiconductor layers, widely used in optoelectronics like LEDs.

  • It precisely controls gas reactions and layer growth, enabling accurate semiconductor layer fabrication.

  • Compared to other methods, MOVPE offers higher uniformity and purity in material production, essential for crafting advanced electronic and optoelectronic devices.

Basic process for MOPVE inside a vacuum chamber

Basic process for MOPVE inside a vacuum chamber

Metalorganic Vapor-Phase Epitaxy (MOVPE) is a specialized subset of chemical vapor deposition. This technique is used for producing both single and polycrystalline thin films. Its primary application lies in the growth of crystalline layers, which are used in creating complex semiconductor multilayer structures. Specifically, this method is useful for creating devices that incorporate alloys in a thermodynamically metastable state. Also known by names like Organometallic Vapor-Phase Epitaxy (OMVPE) or Metalorganic Chemical Vapor Deposition (MOCVD), its use has grown considerably in the production of optoelectronic devices, including the widely used Light-Emitting Diodes (LEDs).

MOPVE Steps 

Preparation

The substrate, typically silicon or sapphire, is prepared and placed inside a reaction chamber.

Gas Introduction

Precursor gases, which are metalorganic compounds and hydrides, are introduced into the chamber. These gases contain elements needed for the semiconductor material.

Reaction

Upon heating, the gases react on the substrate's surface, leading to the deposition of a very thin layer of semiconductor material.

Layer Growth

By controlling the gas flow and temperature, layers of semiconductor material are grown to precise thicknesses and compositions.

Doping

During the process, doping materials can be introduced to alter the electrical properties of the semiconductor layers.

Cooling and Removal

After the desired thickness is achieved, the substrate is cooled and removed from the chamber.

MOPVE Basics

In the Metalorganic Vapor-Phase Epitaxy process, ultrapure precursor gases are introduced into a reactor, often accompanied by a non-reactive carrier gas. When fabricating III-V semiconductors, a metalorganic compound serves as the precursor for the group III elements, while a hydride is used for the group V elements. For instance, to grow indium phosphide, precursors such as trimethylindium ((CH3)3In) and phosphine (PH3) are employed.

As these precursor gases arrive at the semiconductor wafer, they undergo a process known as pyrolysis. During this stage, the subspecies generated from pyrolysis adhere to the surface of the semiconductor wafer. The surface reaction involving these precursor subspecies leads to the integration of specific elements into a new epitaxial layer, fitting into the semiconductor's crystal lattice. MOCVD reactors primarily function in a mass-transport-limited growth regime, where the growth of the layers is propelled by the supersaturation of chemical species in the vapor phase. This technique is versatile, capable of growing films that comprise combinations of elements from groups III and V, groups II and VI, as well as group IV.

MOPVE Process Notes

The chamber used in the Metalorganic Chemical Vapor Deposition (MOCVD) process consists of several key components. These include the reactor walls, a liner, a susceptor, gas injection units, and units dedicated to temperature control. At the heart of this setup, a substrate is carefully positioned on the susceptor, which maintains a precisely controlled temperature. The susceptor itself is crafted from materials that can withstand high temperatures and the reactive nature of the metalorganic compounds utilized in the process.

The introduction of gas into the chamber is facilitated through devices known as bubblers, which are part of a gas inlet and switching system. Additionally, maintaining the appropriate pressure within the chamber is crucial and managed by a specialized pressure maintenance system. This system includes a gas exhaust and cleaning mechanism, which is vital for handling toxic waste products. These waste products are preferably converted into liquid or solid forms for recycling purposes for safe disposal.

MBE vs. MOPVE

Unlike Molecular-Beam Epitaxy (MBE), where crystal growth occurs through physical deposition, in this process, crystals develop through chemical reactions. These reactions don't happen in a vacuum; instead, they occur in the gas phase, operating under moderate pressures ranging from 10 to 760 Torr.

Metalorganic Vapor-Phase Epitaxy for Semiconductors

Metalorganic Vapor-Phase Epitaxy (MOVPE) plays a role in crafting compound semiconductors, which are integral to a wide array of electronic and optoelectronic devices. This technology is used for manufacturing devices such as GaAs-based communication devices, GaN-based LEDs, and lasers used in telecommunications and DVD players. 

MOVPE is particularly valued for its capacity to generate complex device structures, along with its consistent delivery of high uniformity and purity in materials. This makes it a cornerstone technique in semiconductor fabrication, especially for III-V and II-VI devices.

MOVPE is instrumental in producing III-V compound semiconductor heterostructure materials, widely used in optoelectronics, photovoltaics, and high-speed electronics. These materials include quantum structures like quantum wells, wires, and dots, all achievable through this system. There is significant research potential in enhancing and comprehending the growth processes of these materials. Various III-V semiconductors, material systems like AlGaAs/GaAs, GaInP/GaAs, InGaAs/InP, and AlGaInP/GaAs are particularly crucial for quantum well-based optoelectronic devices.

In terms of other applications, MOPVE is integral in:

  • LEDs and lasers, enabling the creation of high-efficiency light-emitting diodes (LEDs) and laser diodes, notably in the visible and UV spectra.

  • Solar cells, including those based on III-V semiconductors.

  • High-frequency and high-power transistor devices like HEMTs (High Electron Mobility Transistors).

  • Complex, multi-layered structures in integrated circuits for advanced electronic applications.

Specific Results

MOPVE has already been used in a variety of specific applications:

  • The GaAs/AlAs Distributed Bragg Reflector (DBR), consisting of multiple layers with alternating refractive indices, designed for specific light absorption or reflection. An example is a 15-layer AlAs/GaAs DBR, grown in a MOVPE system is designed to reflect green light.

  • GaAs/AlGaAs multi-quantum wells (MQW) are created by sandwiching a thin low bandgap semiconductor between two high bandgap layers, focusing on uniform thickness and high-quality crystalline structure with a controlled thickness and interface quality.

  • Materials like AlN, GaAs/AlGaAs, and InP are crucial in advanced semiconductor applications, ranging from UV emitters and VCSELs to high-frequency transistors, infrared detectors, and various photovoltaic devices, underlining their versatility and wide-ranging utility.

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