Advances in the LED Materials and Architectures for Energy-Saving Solid-State Lighting Toward “Lighting Revolution”

Abstract

In this paper, we review the recent developments (in years 2010-2011) of energysaving solid-state lighting. The industry of white light-emitting diodes (LEDs) has made significant progress, and today, white LED market is increasing (mostly with increasing LED screen and LED TV sales). The so-called Blighting revolution[ has not yet really happened on a wide scale because of the lighting efficiency at a given ownership cost. Nevertheless, the rapid development of the white LEDs is expected to soon trigger and expand the revolution.Index Terms: Solid-state lighting, light-emitting diodes, III-nitride.Over centuries, artificial lighting technology has made an incredible progress from candles and gas and kerosene lamps to today's incandescent and fluorescent lighting. As a result, the overall operating cost of light has been reduced by 4.3 orders of magnitude since the 1700s [1], [2]. However, this technological progress has also inevitably increased the consumption of light as the cost of light has decreased. Today, the world uses about 0.72% of its Gross Domestic Product (GDP) on light, for example, in 2010, World GDP of 63.12 T$ (current U.S. $), which means about 455 B$ for artificial lighting. Additionally, as the cost of light has decreased and GDP per capita has increased, the consumption of light per capita has also increased (almost linearly) over time. Over the last three centuries, the consumption of light per capita has increased by 5.4 orders of magnitude. Today, this has reached such a high level that an average person in a well-developed part of the world is effectively surrounded by tens of 100 W light bulbs at all times during his/her waking hours. Therefore, today, too much artificial light is consumed, which costs too much energy. According to a 2006 report by the International Energy Agency (IEA) and the Organization for Economic Co-operation and Development (OECD), lighting is responsible for $19% of electricity consumption and $6% of carbon emission. For our modern civilization today, energy-saving lighting is therefore increasingly essential. Efficient artificial lighting could save billions of dollars and reduce

On the Effect of Step-Doped Quantum Barriers in InGaN/GaN Light Emitting Diodes

“…Accordingly, the electric field at "A" site in Device II can be given by (2) [refer to Fig. 6(c)], while it can be expressed in (3) for Device III if the diffused from the doped part in the quantum barrier is negligible compared to as shown in Fig.…”

“…3(a)]. Moreover, the more increased in Device III compared to Device II is attributed to the reduced electric field at "A" site compared to Device II, as a reduced field at "A" site that is caused by the absence of ionized Si dopants [refer to (2) and (3)] tilts the conduction band more (Fig. 6(e), meV for Device II and 50 meV for Device III) and pushes the electron wave function towards "B" site more [ Fig.…”

“…However, the efficiency is substantially reduced under elevated current injection, and yet high current is required in most of the lighting applications [2]. This effect is well recognized as the efficiency droop.…”

On the origin of the electron blocking effect by an n-type AlGaN electron blocking layer

“…InGaN/GaN multiple quantum well (MQW) lightemitting diodes (LEDs) have made significant progress in the past three decades. [1][2][3] The device performance is, however, still limited by Auger recombination, 4,5 charge separation, 6-9 current crowding, [10][11][12] insufficient hole injection, 9,[13][14][15][16][17][18] and electron overflow from the MQW active region. [19][20][21][22] In order to address these issues, a staggered quantum well architecture and also InGaN/GaN MQWs with Si-step-doped quantum barriers have been proposed to screen the quantum confined Stark effect (QCSE) and increase the spatial overlap of electron-hole wave functions, [7][8][9] while an improved current spreading can be obtained either by making the p-type layer more resistive or the p-contact layer more conductive.…”

Development of multi-colored LED system for therapeutic application

“…The developed multi-colored LED system can generate more than 70 colors and overcome the weakness of the conventional single LED which emits only one color. Many studies have been reported in measuring the information of the light source [17][18][19]. Most of them were to identify the color temperature, luminance, and color rendering index using a spectrometer.…”