Читать книгу VCSEL Industry - Babu Dayal Padullaparthi - Страница 21

Based on the principle of light amplification in semiconductors, the first semiconductor laser was realized by four groups almost simultaneously in 1962. This was two years later after Therdore Maiman demonstrated the first laser [1]. The optical gain layer was located near the p‐n homo‐junction parallel to the substrate [2–5]. The light resonance occurs between the mirrors formed at the edge of the substrate by cleaving or polishing the semiconductor crystal. These lasers are known as edge‐emitting lasers (EELs).

In 1970, eight years later, two groups reported a double heterostructure (DH)‐based laser that enabled room‐temperature continuous operation [6, 7]. The device using an AlGaAs‐GaAs DH structure, as shown in Figure 1.4, introduced by Hayashi and Panish reduced the threshold current density to about 1 kA/cm² at 300 K, a major breakthrough over the initial homo‐junction devices.

Figure 1.4 Double heterostructure laser. (a) The carrier densities of electron and holes in p, i, and n regions. (b) The optical field intensity near the double heterostructure.

Source: [8]. [Image courtesy of Genichi Hatakoshi.]

Back in 1963, a double heterostructure laser had been proposed by Herbert Kromer by using semiconductor layers with varying bandgap and refractive index [9]. Herbert Kroemer and Zhores Alferov [7] both received the 2000 Nobel Prize in Physics for the idea.

This DH structure is used only for confining light field as shown in Figure 1.4b. More descriptions can be found in related textbooks [10–14].